青岛大学信号与系统考研真题2015—2017年
青岛大学信号与系统第八章离散时间系统的z域分析
则
Z [an x(n)] X ( z ) a
z , Rx1 a Rx2
特别地 Z [(1)n x(n)] X (z) , Rx1 z Rx2
例：Z
[cos(0n)u(n)]
z(z cos0 ) z2 2z cos0 1
, z 1
Z
[ n cos(0n)u(n)]
z
(z
cos0 )
2
2
nu(n)
z
d dz
z
z 1
(z
z 1)2
n2u(n)
z
d dz
(z
z 1)2
z(z 1) (z 1)3
X (z) 1 [ z z(z 1)] z2 2 (z 1)2 (z 1)3 (z 1)3
, z 1
（四）序列指数加权（ z 域尺度变换）
若 Z [x(n)] X (z) , Rx1 z Rx2
X (z) Z [x(nT )] x(nT )zn n
2T 0 T 3T
t
L [xs (t)] z esT Z [x(nT )]
z
esT
r eT
T 2
s
z re j s j
T—— 抽样间隔，
s
2
T
——
抽样角频率
z平面和 s平面的映射关系：
1. s平面原点 ( 0, 0) j
x(1) (n)
0
n
x(n 1)u(n) x(n 1)u(n 1)
x(0) (n 1)
0
n
x(n 1)u(n) x(n 1)u(n 1) x(1) (n) x(n 1)u(n) x(n 1)u(n 1) x(0) (n 1) x(n 2)u(n) x(n 2)u(n 2) x(2) (n) x(1) (n 1) x(n 2)u(n) x(n 2)u(n 2) x(0) (n 2) x(1) (n 1)
青岛大学考研专业课真题——信号与系统 2010年 (附带答案及评分标准)
科目代码： 827 科目名称： 信号与系统 （共 13 页）请考生写明题号，将答案全部答在答题纸上，答在试卷上无效Ⅰ、单项选择题（每题3分，共7题，21分）1．题图1所示)(t f 为原始信号，)(1t f 为变换信号，则)(1t f 的表达式为( )。
A ．(22)f t -+B ．(21)f t --C ．)12(+-t fD ．(22)f t --2．(2)t dt δ∞-∞=⎰( )，其中()t δ为单位冲激信号。
A ．1B ．12C ． 2D ． ()u t3．一个理想低通滤波器由冲激响应)()(Bt Sa t h =描述，由于)(t h 在0<t 内不等于零并且)(Sa 函数不是绝对可积的，因此理想低通滤波器是( )。
A ．因果的、稳定的 B ．非因果的、稳定的 C ．因果的、不稳定的 D ．非因果的、不稳定的 4．给定系统微分方程、起始状态以及激励信号分别为22()3()2()()d d d r t r t r t e t dtdtdt++=，(0)1r -=、(0)1r -'=，()()e t u t =则下列说法正确的是( )。
A ． 系统在起始点发生跳变，(0)1r +=、(0)3r +'=B ． 系统在起始点不发生跳变，(0)1r +=C ． 系统在起始点发生跳变，(0)1r +=、(0)2r +'=D ． 系统在起始点不发生跳变，(0)1r +=、(0)1r +'=题图12 0 2t1 3)(1t f )(t f 02t-4 -2科目代码： 827 科目名称： 信号与系统 （共 13 页）请考生写明题号，将答案全部答在答题纸上，答在试卷上无效5．在下面方程所描述的系统中，只有( )是时不变系统。
其中()e t 是输入信号，()r t 是输出信号。
A ．()()()r t e t u t =B ． ()(1)r t e t =-C ．2()()r t e t =D ． ()(2)r t e t =6．下列系统函数所描述的因果线性时不变离散时间系统中，构成全通网络的是（ ）。
青岛大学2020年827信号与系统
信号与信息处理专业硕士入学考试大纲
考试科目代码及名称：827信号与系统
一、考试要求
掌握连续时间信号与系统分析的基本理论，掌握离散信号分析、离散时间系统设计的基本理论和方法，具备从事实际信号分析与处理工作的基本能力。
二、考试内容
（1）信号的运算和分解
（2）连续线性时不变系统的时域经典分析
（3）系统模型与系统框图
（4）单位冲激响应与卷积
（5）傅里叶变换与采样定理
（6）拉普拉斯变换与连续系统的s域分析
（7）系统函数与频率响应
（8）信号无失真传输、调制与解调
（9）离散时间系统的时域经典分析
（10）序列的z变换与离散傅里叶变换
三、试卷结构（题型分值）
1.本科目满分为150分，考试时间为180分钟。
2.题型结构
（1）选择题：占总分的16%
（2）填空题: 占总分的16%
（3）计算题：占总分的68%
四、参考书目
《信号与系统引论》，郑君里应启珩杨为理，高等教育出版社，出版时间2018-12-10。
青岛大学考研专业课真题——信号与系统 2007年 (附带答案及评分标准)
科目代码： 827 科目名称： 信号与系统 （共 12 页）请考生写明题号，将答案全部答在答题纸上，答在试卷上无效Ⅰ、填空题（共14题，每题3分，共42分）1．积分=-'+⎰∞∞-dt t t )1()2(2δ 。
2．如图1所示，)(t f 为原始信号，)(1t f 为变换信号，则)(1t f 的表达式为 （用)(t f 表示）。
3．若正弦序列0sin()n ω的周期10N =，则0ω的最小取值为0ω= 。
4． 给定微分方程、起始状态、激励信号分别为()2()3()d d r t r t e t dtdt+=、(0)0r -=、()()e t u t =，则(0)r += 。
5．已知)4()()()(--==n u n u n h n x ，则卷积和序列)()()(n h n x n y *=共有 个非零取值。
6．单边拉氏变换21()(2)F s s =+对应的原函数为=)(t f 。
7．图2所示因果周期矩形脉冲的拉氏变换()F s = 。
8．序列||1()2n x n ⎛⎫= ⎪⎝⎭的z 变换及其收敛域为 。
图12 0 )(t f 2t 1 3)(1t f 2t-4 -2图22TT )(t ft1T 2…科目代码： 827 科目名称： 信号与系统 （共 12 页）请考生写明题号，将答案全部答在答题纸上，答在试卷上无效9．若象函数2()(1)z F z z =-，1z <，则原序列=)(n f 。
10．调幅信号26()(100)cos(10)f t Sa t t ππ=⋅的频带宽度为 Hz 。
11．若离散线性时不变系统的单位样值响应()()2(1)3(2)(3)h n n n n n δδδδ=+---+-，则单位阶跃响应()g n 的序列波形为。
12．若某线性时不变离散时间系统的单位样值响应为)(2)1(3)(n u n u n h n n -+--=，则该系统是（因果/非因果、稳定/非稳定）系统。
青岛大学概率论及数理统计一考研真题2015—2017年
0 x y 1; 其它.
求 (X ,Y) 分别关于 X 和Y 的边缘概率密度 fx x, fy y 。
5：(15 分) 已知随机变量 X N 0, 2 ，Y 在区间 0, 3 上服从均匀分
布，且 D X Y 2 ，求 X 和Y 的相关系数 。
3
2
2）若该机床已停机，求它是在加工零件 A 时发生停机的概率。 七、（15 分）设事件 A, B 及 A B 的概率分别为 p 、q 及 r ，求 P( AB) ，P( AB) ， P( AB) ， P( AB) 。
3
青岛大学 2016 年硕士研究生入学考试试题
科目代码： 619 科目名称：概率论及数理统计 （共 3 页） 请考生写明题号，将答案答在答题纸上，答在试卷上无效
2. 随机变量 X 与 Y 相互独立，且方差为 D X 4 ， D Y 2 ，则方差
D 3X 2Y ＝________.
3. 一个袋子中有相同大小的红球 6 只、黑球 4 只，从中不放回地抽取 2
只，则第一次和第二次都取到红色球的概率为
。
4. 设 E(X ) 2 , E(Y ) 3 , 则 E(X Y 5)
EX ______。
，则
2、(4 分) 设 A、B、C 是三个随机事件，则“事件 A、B、C 不多于一个发
生”的逆事件是________。
3、（4 分）设 P(A) 0.5, P(B) 0.6, P(A B) 0.9 ,则 P(B | A) __________.
4、（4
分）随机变量 X
的概率密度函数
4x2 4K x K 2 有0 根的判别式所决定有实根的概率。 3：(15 分) 设随机变量 X 具有密度函数 f (x) 1 e|x| ， x ，求 X
信号与系统 第二章习题 王老师经典解法(青岛大学)小白发布
2-16 已知 f1 (t ) =
画出下列各卷积的波形。 （1） s1 (t ) = f1 (t ) ∗ f 2 (t ) ； （2） s2 (t ) = f1 (t ) ∗ f 2 (t ) ∗ f 2 (t ) ； （3） s3 (t ) = f1 (t ) ∗ f 3 (t ) 。
2-17 求题图 2-17 所示电路在 e(t ) = (1 + 2e
第二章
连续时间系统的时域分析
2-1 电路如题图 2-1 所示，列写求 vo (t ) 的微分 方程。
L1 1H R1 2Ω + e(t) i 1 (t )
R2 1Ω + L2 2H 题图 2-1
C
1F
i 2 (t )
vo(t)
2-2 电路如题图 2-2 所示， 列写求 i2 (t ) 的微分方 程。
题图 2-18
−2 t
− 1)U (t ) ， 试利用卷积的性质求题
1 0 -1
e2(t)=tU(t) 1 t 0
e3(t)
t 0 1
2-19 一线性时不变的连续时间系统，其初始状态一定，当输入 e1 (t ) = δ (t ) 时，其全响应
r1 (t ) = −3e − tU (t ) ； 当 输 入 e2 (t ) = U (t ) 时 ， 其 全 响 应 r2 (t ) = (1 − 5e − t )U (t ) 。 求 当 输 入 e(t ) = tU (t ) 时的全响应。
2-14 计算卷积 f (t ) = f 1 (t ) ∗ f 2 (t ) ，其中 f1 (t ) = sgn(t − 1) ， f 2 (t ) = e 2-15 求下列卷积 （1） f1 (t ) = e
信号与系统 第四章习题 王老师经典解法(青岛大学)小白发布
3
E1(s)
∑
1 s
-2 -1
（a）
1 s
2
∑
Y 1( s )
E2(s)
−2 t
Vo ( s ) ； E ( s)
U (t ) ，求零状态响应 vo (t ) ；
（3）若 e(t ) = 10 cos(5t ) ，求正弦稳态响应 voss (t ) 。
0.25F + e(t) -
2:1
1F
2:1
2F +
C1
C2
C3
R
vo(t
-
题图 4-17-1
4-18 题图 4-18-1 所示电路 （1）若初始无储能，信号源为 is (t ) ，为求 i1 (t ) （零状态响应） ，列写转移函数 H ( s ) ，并给 出对应于 is (t ) = 10 cos(2t )U (t ) 的零状态响应 i1 (t ) ； （2）若初始状态以 i1 (0) ， v 2 (0) 表示（都不等于零） ，但
is(t
)
1Ω + 1F
-
1H
i1(t
is (t ) = 0 ，求 i1 (t ) （零输入响应） 。
v 2( t )
1Ω
题图 4-18-1
4-19 求题图 4-19 中电路的电压传输函数，如果要求响应中不出现 强迫响应分量，激励函数应有怎样的模式？
C
R1
+ +
-)
e(t R2
vo(t)
-
题图 4-19
4-11 用拉氏变换分析法，求下列系统的响应。
d 2 r (t ) dr (t ) （1） +3 + 2r (t ) = 0 ， r (0 − ) = 1 ， r ' (0 − ) = 2 2 dt dt
信号与系统第二章_连续时间系统时域分析(青岛大学)
n
rzi (t) Azikekt k 1
（b）
r(k zi
)
(0
)
r(k) (0 )
k 0,1,L ,(n 1)
系数Azik可直接由 r(k) (0 ) 来确定。
例：已知描述某二阶LTI连续时间系统的动态方程
d2 dt 2
r(t)
5
d dt
r(t)
6r(t)
e(t)
起始状态 r(0 ) 1,r(0 ) ，2激励信号
(t)
2
p3
5
2p p2
5
p
3
e(t)
2
d3 dt3
vo
(t)
5
d2 dt 2
vo
(t)
5
d dt
vo
(t)
3vo
(t)
2
d dt
e(t)
总结： （1）引入算子符号后，RLC 电路可借助纯电阻电路的分析方法；
（2）是否可消去公共因子的原则：微分方程的阶数应等于电路 阶数（独立储能元件的个数）。
§2.3 微分方程的经典解法 r(t) rh (t) rp (t)
r(0 ) r(0 ) 1
（4）由 0状态确定待定系数
r(t) A1et A2e2t 0.5e3t
rr((00))
A1 A1
A2 0.5 1 2A2 1.5
3
A1 A2
5.5 5
全响应 r(t) 5.5et 5e2t 0.5e3t ,t 0
（一）经典法求解微分方程步骤：
r(t) 0 u(t) r(0 ) r(0 )
代入
d2 dt 2
r(t)
3
d dt
r(t)
青岛理工大学信号与系统考题
青岛理工大学试卷标准答案及评分标准专用纸2009 ~ 2010_学年第 一 学期 信号与系统 课程试卷标准答案及评分标准 A( )/B(√) 卷专业_______________ 班级 _____________一、简单计算题 (每题5分，共55分)1.2. 线性、时变、非因果。
3. ()13H s s =+，d ()3()()d r t r te t t+=。
4. ()()23123e etth r t A t A A --=++。
5. ()21r P N w RC π=+6.7.幅度谱 相位谱8. 1234223344234122332244()1H H H H H s H G H G H G H H H G H G H G H G H G =++++++。
青岛理工大学试卷标准答案及评分标准专用纸9. 状态方程：()112233 3 2 10 0 2 10 0 0 11e t λλλλλλ⎡⎤-⎡⎤⎡⎤⎡⎤⎢⎥⎢⎥⎢⎥⎢⎥=-+⎢⎥⎢⎥⎢⎥⎢⎥⎢⎥⎢⎥⎢⎥⎢⎥-⎣⎦⎣⎦⎣⎦⎣⎦ ；输出方程：()[]1231,0,0 r t λλλ⎡⎤⎢⎥=⎢⎥⎢⎥⎣⎦。
10. 2(1)1()1s F s es -+=+。
11.()()()()()()2222dd dd 71064d d d d i t i t i t e t e t e t tttt++=++。
二、（共10分）1. 最小抽样频率m in 3000f =Hz 和最大抽样间隔m ax 13000T =s 。
（5分）2.三、（共15分）1. 4()3H s s =+。
（5分）2. 极点全部在左半平面，系统稳定；极点全部在左半平面和虚轴上，且在虚轴上的极点为一阶极点，系统临界稳定；只要有一个极点在右半平面和虚轴上（二阶和二阶以上），系统不稳定（3分）。
该系统极点在左半平面，所以系统稳定（2分）。
3. 4()3H jw jw =+（2分），系统的幅频特性曲线如下图所示（2分），可知该系统为低通滤波器（1分）。
【青岛大学2012年考研专业课真题】信号与系统2012
4
科目代码： 827 科目名称： 信号与系统 （共
4
页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
e(t ) e3t u(t ) ，则 r (0 )
。
9 ．若可逆系统的单位冲激响应为 h(t ) ，其逆系统的单位冲激响应为 hI (t ) ，则
h(t ) hI (t )
。
10．图 3 所示以 f (t ) 为输入， g (t ) 为输出的对 调幅波进行相干解调的系统是 （线性/非线性） 、 的。 （时变/时不变）
f (t )
低通滤波
g (t )
cos(0t )
图3
二、 （15 分）计算图 4 所示矩形脉冲信号 h(t ) 和半波正弦脉冲信号 e(t ) 的卷积积 分 r (t ) h(t ) e(t ) ，并画出 r (t ) 的波形。
f e (t ) =
， f o (t ) =
。 。
Hz ，
3．若正弦序列 sin(0 n) 的周期 N 10 ，则 0 的最小取值为 0 4．周期矩形脉冲信号 f (t ) 如图 1 所示，则该信号的谱线间隔为 直流分量为 。
1 … -10 -1 0 1 图1 10
f (t )
…
t
5．频谱函数 F () j sgn() 的傅里叶逆变换 f (t ) 6 ．图 2 所示因果周期信号的拉氏变换 F ( s) 为 。
f (t )
1 0 1 2 3
图2
。 ，对应的收敛域
4
5
6
t
1 7．序列 ( ) n u (n) 的 z 变换 X ( z ) 2
8．给定微分方程、起始状态、激励信号分别为
青岛大学2015年硕士研究生入学考试初试试题考试科目：642基础英语
青岛大学2015年硕士研究生入学考试试题科目代码： 642 科目名称：基础英语(共12页）请考生写明题号，将答案全部答在答题纸上，答在试卷上无效PART I SENTENCE COMPLETION (30 points )Choose the word or the set of words that, when inserted in the sentence, best fits the meaning of the sentence as a whole.1. Like a credit card in appearance, the smart card contains a microchip that stores digital tokens which can be exchanged for goods, just like ______ cash.A. concreteB. tentativeC. tangibleD. intact2. The Team of England, who are now superbly fit, will be doing their best next week to______ themselves for last year’s defeat.A. reviveB. retortC. revenge D remedy3. When Tastuma first came to the US from Japan, he wasn’t sure he could ______ intothe American culture, but after a few months , he felt at home here.A. absorbB. transformC. digest D assimilate4. The constitution of the State required that property should be _____ for taxation at itsmarket value.A. estimatedB. appraisedC. evaluatedD. valued5. The idealized paintings of nature produced in the 18th century are evidence thatmedieval ______ natural settings had been ______and that the outdoors now could be enjoyed without trepidation.A. fear of …exorcisedB. concerns about …regainedC. affection for …surmountedD. disinterest in …alleviated6. Edith Wharton sought in her memoir to present herself as having achieved a harmonious wholeness by having ________ the conflicting elements of her life.A.affirmedB. highlightedC. reconciledD. confined7. In the 20th century, the discovery of radium _____ the popular imagination; not only was its discoverer, Marie Curie, idolized, but its market value ______ that of the rarest gemstone.A. stormed … diminishedB. horrified …approachedC. enflamed… exceededD. conspired… triggered8. Since the 15th century, animals have been used as ____ for people in experiments to assess the effects of therapeutic and other agents that might later be used in humans.A. benefactorsB. companionsC. surrogatesD. precedents9. Issues of price, place, promotion, and product are _______ conventional concerns in planning marketing strategies.A. these of the mostB. most of thoseC. among the mostD. among the many of10. The disagreement over the trade restrictions could seriously _______ relations between the two countries.A. tumbleB. jeopardizeC. manipulateD. intimidate11. New research raises new concerns that altering crops to withstand such treats maypose new risks---from _____the weeds themselves.A. anything butB. other thanC. more thanD. none other than12. In this small village, he found few persons ___ to him and felt quite lonely.A. congenitalB. contentiousC. congenialD. Concurrent13. The chief reason for the population growth isn’t so much a rise in birth rates ____ afall in death rates as a result of improvements in medical care.A. andB. as C but D or14. Bipartisan bills are pending in Congress that would eliminate all travel restrictionsand ______ the embargo.A. freeB. slackenC. unwindD. ease15. Rather than enhancing a country's security, the successful development of nuclearweapons could serve at first to increase that country's ________.A.boldnessB.influenceC. responsibilityD. vulnerability16. Although scientists claim that the seemingly ________ language of their reports ismore precise than the figurative language of fiction, the language of science, like all language, is inherently ________.A.ornamental ... subtleB. unidimensional ... unintelligibleC. symbolic ... complexD. literal ... allusive17. Laws do not ensure social order since laws can always be ________, which makesthem ________ unless the authorities have the will and the power to detect andpunish wrongdoing.A.contested ... provisionalB. circumvented ... antiquatedB.repealed ... vulnerable D. violated ... ineffective18. The pressure of population on available resources is the key to understanding history;consequently, any historical writing that takes no cognizance of______ factsis______ flawed.A.demographic….intrinsicallyB.ecological…. marginallyC. cultural…..substantivelyD. psychological…philosophically19. By putting billions of dollars into the ailing automaker, the Obama administrationhas placed a huge bet on the effort to revive and _____ the company through the elimination of brands, dealerships and factories.A. streamlineB. strayC. strikeD. strife20. Under the deal, the union’s cost-of-living interests, performance bonuses and someholiday pay will be _____ to offset health-care costs.A. sustainB. retakeC. swabD. suspend21. The capital intended to broaden the export base and ____efficiency gains frominternational trade was channeled instead into uneconomic import substitution.A. secureB. extendC. defendD. possess22. New sources of energy must be found, and this will take time, but it is not likely toresult in any situation that will ever restore that sense of cheap and _____ energy we have had in the times past.A. exquisiteB. resilientC. copiousD. formidable23. Gaddis is a formidably talented writer whose work has been, unhappily, more likelyto intimidate or his readers than to lure them into his fictional world.A. enticeB. strengthenC. transformD. repel24. Her is always a source of irritation: she never uses a single word when shecan substitute a long clause or phrase in its place.A. verbosityB. simplicityC. cogencyD. rhetoric25. If those large publishers that respond solely to popular literary trends continue todominate the publishing market, the initial publication of new writers will depend on the writer’s willingness to________ popular tastes.A. struggle againstB. cater toC. admireD. flout26. Contrary to the popular conception that it is powered by conscious objectivity,science often operates through error, happy accidents, ________ and persistence in spite of mistakes.A. controlsB. hunchesC. deductionsD. calculations27. By putting the entire Woolf archive on a microfilm, the project directors hope tomake the contents of manuscripts more _____ to scholars.A.objectiveB. accessibleC. appealingD. implicit28. Despite the ________ of many of their colleagues, some scholars have begun toemphasize "pop culture" as a key for ________ the myths, hopes, and fears ofcontemporary society.A.antipathy ... entanglingB. discernment ... evaluatingC. skepticism ... decipheringD. pedantry ... reinstating29. The powers and satisfactions of primeval people, though few and meager,were______ their few and simple desires.A.simultaneous withB. commensurate withC. substantiated byD. ruined by30. Social scientists have established fairly clear-cut ________ that describe theappropriate behavior of children and adults, but there seems to be ________ about what constitutes appropriate behavior for adolescents.A.functions ... rigidityB. estimates ... indirectnessC. norms ... confusionD. regulations ... certaintyPART II PROOF READING AND ERROR CORRECTION (10 Points) The following passage contains TEN errors. Each line contains a maximum of ONE error. In each case, only ONE word is involved. You should proofread the passage and correct it in the following way.For a wrong word, underline the wrong word and write the correct one in the blank provided at the end of the line.For a missing word, mark the position of the missing word with a “∧”sign and write the word you believe to be missing in the blank provided at the end of the line.For an unnecessary word cross out the unnecessary word with a slash “/”and put the word in the blank provided at the end of the line.In many states, budget requests by state universities have had tobe scaled back or frozen, while tuition, the share of the cost borne bythe students themselves, has gone up. The problem with the governors (1) __________is particularly distressing because they all agree that the quality oftheir colleges and universities helps drive the economic enginesof their states. And they are constantly being told by everyone like (2) ___________college administrators to editorial writers that only way to make (3)___________their state universities better is to spend more money.But it was against this backdrop that members of the Association(4)___________came together in this city to discuss issues of common concern, oneis higher education. And the focus of their talks about colleges(5)____________centered not on how money could be more effectively directed,but on what to get greater productivity out of a system that has(6)____________become highly inefficient and resistive against change.(7)_____________As a result, the governors will embark a three-year study of (8) _____________higher education system and how to make state colleges anduniversities better able to meet the challenges of a global economy inthe 21st century. And judging from the tenor and tone of theirdiscussion, the study could produce a push in for higher standards, (9) ___________more efficiency and greater accountability. Pennsylvania GovernorTom Ridge and his fellow governors came away from the meetingsresolute with the belief that higher education needs a fresh look and (10) ____________possibly a major boost in productivity to meet demands of newtechnologies and a changing work force.PART III READING COMPREHENSION (30 Points)In this section there are three reading passages followed by a total of fifteen multiple-choice questions. Read the passages and then write your answers on your answer sheet.Passage1Despite Denmark’s manifest virtues, Danes never talk about how proud they are to be Danes. This would sound weird in Danish. When Danes talk to foreigners about Denmark, they always begin by commenting on its tininess, its unimportance , the difficulty of its language, the general small-mindedness and self-indulgence of their countrymen and the high taxes. No Dane would look you in the eye and say, “Denmark is a great country.” You’re supposed to figure this out for yourself.It is the land of the silk safety net, where almost half the national budget goes toward smoothing out life’s inequalities, and there is plenty of money for schools, day care, retraining programmes, job seminars-- Danes love seminars: three days at a study centre hearing about waste management is almost as good as a ski trip. It is a culture bombarded by English, in advertising, pop music, the Internet, and despite all the English that Danish absorbs—there is no Danish Academy to defend against it —old dialects persist in Jutland that can barely be understood by Copenhageners. It is the land where, as the saying goes, “Few have too much and fewer have too little, ”and a foreigner is struck by the sweet egalitarianism that prevails, where the lowliest clerkgives you a level gaze, where Sir and Madame have disappeared from common usage, even Mr. and Mrs. It’ s a nation of recyclers—about 55 % of Danish garbage gets made into something new—and no nuclear power plants. It’s a nation of tireless planner.Trains run on time. Things operate well in general.Such a nation of overachievers —a brochure from the Ministry of Business and Industry says, “Denmark is one of the world’s cleanest and most organize d countries, with virtually no pollution, crime, or poverty. Denmark is the most corruption-free society in the Northern Hemisphere.”So, of course, one’s heart lifts at any sighting of Danish sleaze: skinhead graffiti on buildings (“Foreigners Out of Denmark! ”), brokenNonetheless, it is an orderly land. You drive through a Danish town, it comes to an end at a stone wall, and on the other side is a field of barley, a nice clean line: town here, country there. It is not a nation of jay-walkers. People stand on the curb and wait for the red light t o change, even if it’s 2 a.m. and there’s not a car in sight. However, Danes don’ t think of themselves as a wait- ing-at-2-a.m.-for-the-green-light people——th at’s how they see Swedes and Germans. Danes see themselves as jazzy people, improvisers, more free spirited than Swedes, but the truth is (though one should not say it)that Danes are very much like Germans and Swedes. Orderliness is a main selling point. Denmark has few natural resources, limited manufacturing capability; its future in Europe will be as a broker, banker, and distributor of goods. You send your goods by container ship to Copenhagen, and these bright, young, English-speaking, utterly honest, highly disciplined people will get your goods around to Scandinavia, the Baltic States, and Russia. Airports, seaports, highways, and rail lines are ultramodern and well-The orderliness of the society doesn’t mea n that Danish lives are less messy or lonely than yours or mine, and no Dane would tell you so. You can hear plenty about bitter family feuds and the sorrows of alcoholism and about perfectly sensible people who went off one day and killed themselves. An orderly society can not exempt itsBut there is a sense of entitlement and security that Danes grow up with. Certain things are yours by virtue of citizenshi p, and you shouldn’t feel bad fo r taking what you’re entitled to, you’re as good as anyone else. The rules of the welfare system are clear to everyone, the benefits you get if you lose your job, the steps you take to get a new one; and the orderliness of the system makes it possible for the country to weather high unemployment and social unrest without a sense of crisis.1. The author thinks that Danes adopt a ___ attitude towards their country.A. boastfulB. modestC. deprecating2. Which of the following is NOT a Danish characteristic cited in the paA. Fondness of foreign culture.C. Linguistic tolerance.D. Persistent planning.3. The author’s reaction to the statemen t by the Ministry of Business and Industry is ___.A. disapprovingB. approving D. doubtful4D. prevents Danes from acknowledg5. At the end of the passage the author states all the following EXCEPT thatC. the open system helps to tide the couPassage 2Education is an important theme in youth athletics in the US. Young kids, energetic, noisy, uncontrollable, confined to class, yearn for the relative freedom of the football field, the basketball court, the baseball diamond. They long to kick and throw things and tackle each other, and the fields of organized play offer a place in which to act out these impulses. Kids are basically encouraged, after all, to beat each other up in the football field. Yet for all the chaos, adult guidance and supervision are never far off, and time spent on the athletic fields is meant to be productive. Conscientious coaches seek to impart lessons in teamwork, self-sacrifice, competition, gracious winning and losing. Teachers at least want their pupils worn out so they’ll sit still in reading class.By the time children start competing for spots on junior high soccer teams or tennis squads, the kids’ gloves have come off to some extent. The athletic fields become less a place to learn about soft values like teamwork than about hard self-discipline and competition. Competitiveness, after all, is prized highly by Americans, perhaps more so than by other peoples. For a child, being cut from the hockey team or denied a spot on the swimming is a grave disappointment—— and perhaps an opportunity for emotional or spiritual growth.High school basketball or football teams are places where the ethos of competition is given still stronger emphasis. Although high school coaches still consider themselves educators, the sports they oversee are not simple extensions of the classroom. They are important social institutions, for football games bring people together. In much of the US they are events where young people and their elders mingle and see how the community is evolving.For the best players, the progression from little league to junior high to high schoolleads to a scholarship at a famous college and maybe, one day, a shot at the pros. To all appearances, college athletes are student-athletes, an ideal that suggests a balance between the intellectual rigors of the university and the physical rigors of the playing field. The reality is skewed heavily in favor of athletics. One would have difficulty showing that major US college sports are about education. Coaches require far too much of players’ time to be truly concerned with any thing other than performance in sport. Too often, the players they recruit seem to care little about school themselves.This was not always the case. Universities — Princeton, Harvard, Rutgers, Yale —were the birthplaces of American football and baseball; education—the formation of “character” —was an important part of what those coaches and players thought they were achieving. In 1913, when football was almost outlawed in the US, the game’s most prominent figures traveled to Washington and argued successfully that football was an essential part of the campus experience and that the nation would be robbed of its boldest young men, its best potential leaders, if the game were banned.The idea that competitive sports build character, a western tradition dating from ancient Greece, has evidently fallen out of fashion in today’s US. Educators, now prone to see the kind of character shaped by football and basketball in dark light, have challenged the notion that college sports produce interesting people. Prominent athletes, such as boxer Muhammad Ali and basketball star Charles Markley, deliberately distanced themselves from the earlier ideal of the athlete as a model figure. Today’s US athlete is thus content to be an entertainer.Trying to do something socially constructive, like being a role model, will make you seem over-earnest and probably hurt your street credibility.When I was a kid, my heroes played on Saturdays: they were high school players and college athletes. Pro football games, broadcast on Sunday afternoons, were dull and uninspiring by comparison. After all, why would God schedule anything important for Sun day? You’ve got school the next day.Although I certainly couldn’t have articulated it at the time, I think I must already have sensed that throwing a ball or catching passes was a fairly pointless thing to be good at. In the grand scheme, it was a silly preparation for a job. Yet playing sports was not pointless; the point, however, was that you were learning something——a disposition, a certain virtue, a capacity of arduous endeavor——that might be of value when you later embarked upon a productive career as a doctor or a schoolteacher or a businessman. The optimism of those Saturday afternoons was infectious. I still feel that way today.6. Pupils mainly learn ______ on the athletic fields.A. soft valuesB. hard valuesC. value for freedomD. value of equality7. In high school basketball or football teamsA. hard values are less emphasizedB. the sports are separated fromclassrooms.C. the social function of sports is prominent.D. the coaches are less of educators.8. Which of the following is NOT true about college sports?A. The best players may end up getting a scholarship at a famous college.B. College athletes have always cared little about school themselves.C. College sports are more in favor of athletics than education.D. The formation of “character” used to be the goal of coaches and players.9. The author’s attitude toward the notion of “athletes as entertainers” isA. positiveB. neutralC. negativeD. impossible to tell.10. The best title for this passage isA. Education System in the USB. Development of Athletics in the USC. US Education in Youth AthleticsD. Development of Education in the US.Passage 3Human migration: the term is vague. What people usually think of is the permanent movement of people from one home to another. More broadly, though, migration means all the ways—from the seasonal drift of agricultural workers within a country to the relocation of refugees from one country to another.Migration is big, dangerous, compelling. It is 60 million Europeans leaving home from the 16th to the 20th centuries. It is some 15 million Hindus, Sikhs, and Muslims swept up in a tumultuous shuffle of the citizens between India and Pakistan after the partition of the subcontinent in 1947.Migration is the dynamic undertow of population change: everyon e’s solution, everyon e’s conflict. As the century turns, migration, with its inevitable economic and political turmoil, has been called “one of the greatest challenges of the coming century.”But it is much more than that. It is , as it has always been, the great adventure of human life. Migration helped create humans, drove us to conquer the planet, shaped our societies, and promised to reshape them again.“You have a history book written in your genes,” said Spencer Wells. The book he is trying to read goes back to long before the first word was written, and it is a story of migration.Wells, a tall, blond geneticist at Stanford University, spent the summer of 1998 exploring remote parts of Transcaucasia and Central Asia with three colleagues in a Land Rover, looking for drops of blood. In the blood, donated by the people he met, he will search for the story that genetic markers can tell of the long paths human life has taken across the Earth.Genetic studies are the latest technique in a long effort of modern humans to find out where they have come from. But however the paths are traced, the basic story issimple: people have been moving since they were people. If early humans hadn't moved and intermingled as much as they did, they probably would have continued to evolve into different species. From beginnings in Africa, most researchers agree, groups of hunter-gatherers spread out, driven to the ends of the Earth.To demographer Kingsley Davis, two things made migration happen. First, human beings, with their tools and language, could adapt to different conditions without having to wait for evolution to make them suitable for a new niche. Second, as populations grew, cultures began to differ, and inequalities developed between groups. The first factor gave us the keys to the door of any room on the planets; the other gave us reasons to use them.Over the centuries, as agriculture spread across the planet, people moved toward places where metal was found and worked and to centres of commerce that then became cities. Those places were, in turn, invaded and overrun by people later generations called barbarians.In between these storm surges were steadier but similarly profound tides in which people moved out to colonize or were captured and brought in as slaves. For a while the population of Athens, that city of legendary enlightenment was as much as 35 percent slaves."What strikes me is how important migration is as a cause and effect in the great world events." Mark Miller, co-author of The Age of Migration and a professor of political science at the University of Delaware, told me recently.It is difficult to think of any great events that did not involve migration. Religions spawned pilgrims or settlers; wars drove refugees before them and made new land available for the conquerors; political upheavals displaced thousands or millions; economic innovations drew workers and entrepreneurs like magnets; environmental disasters like famine or disease pushed their bedraggled survivors anywhere they could replant hope."Its part of our nature, this movement," Miller said, "It's just a fact of the human condition."11. Which of the following statements is INCORRECT?A. Migration exerts a great impact on population change.B. Migration contributes to Mankind’s progress.C. Migration brings about desirable and undesirable effects.D. Migration may not be accompanied by human conflicts.12. What do we know about Spencer Wells from the passage?A. He thought genes can tell where people have come from.B. He wrote a book about the history of genes.C. He read the first history book at Stanford UniversityD. He agreed human migration was from Transcaucasia and central Asia.13. According to Kingsley Davis, migration occurs as a result of the following reasonsEXCEPT ______.A. human adaptabilityB. human evolutionC. cultural differencesD. inter-group inequalities14. Which of the following groups is NOT mentioned as migrants in the passage?A. Farmers.B. Workers.C. Settlers.D. Colonizers.15. There seems to be a(n) ______ relationship between great events and migration.A. looseB. indefiniteC. causalD. remotePART IV TRANSLATION FROM ENGLISH INTO CHINESE (40 Points)What happens to the students who cheat on the two college admissions exam, the SAT and the ACT? Not as much as you might think. It isn’t particularly easy to cheat on these exams, but that doesn’t stop some students from trying. They do it in all the ways you might imagi ne: Copying off someone else’s paper, texting on a cellphone for answers, bringing in cheat sheets, having someone else take the test for them.And some cheat in ways you might not consider: In South Korea, a test prep tutor was investigated for allegedly buying scanned copies of sections of the SAT and then emailing them, with the answers, to South Koreans in Connecticut who were going to take the test 12 hours later. Another SAT tutor in South Korea was arrested for getting students taking the SAT to put test questions into a calculator they were allowed to use, and to hide small blades in their erasers that they used to cut out pages of the test. So, you ask, what happens to students suspected of cheating on the SAT or the ACT?I asked both the College Board, which owns the SA T, and ACT Inc., which owns the ACT, to explain what triggers suspicion of cheating and what happens to students found to be cheating. Ed Co lby, spokesman for the ACT, said he couldn’t tell me exactly how many investigations are conducted each year for security reasons. Tom Ewing, a spokesman for the Educational Testing Service, which administers the SAT for the College Board, said there are a few thousand questionable test scores each year out of more than 2 million tests. Both said a review of a student’s test could be triggered in one of several ways, including an audit that flags scores that have risen dramatically, or by a tip from outside parties, such as a guidance counselor, college admissions officer or NCAA official.PART V WRITING (40 Points)In most countries, with the widespread of the use of Internet, people have more freedom to choose to work and study at home instead of travelling to work or college. Do the advantages outweigh the disadvantages?Write an essay of about 400words, Use specific reasons/examples to support your position on the statement above. In the first part of your writing you should present your thesis statement, and in the second part you should support the thesis statement with appropriate details. In the last part you should bring what you have written to a natural conclusion or make a summary.You should supply an appropriate title for your essay.Marks will be awarded for content, organization, grammar, diction and appropriateness. Failure to follow the above instructions may result in a loss of marks.。
信号与系统 第三章习题 王老师经典解法(青岛大学)小白发布
E E 2
0
−
t
τ
2
0
t2 τ t3 2
题图 3-9-1
τ , t < − t0 E 2 τ f (t ) = π ( t − + t0 ) τ τ E 2 + { 1 cos[ ]} , − t0 ≤ t ≤ + t0 2 2t0 2 2
或写作
τ , t < − t0 E 2 f (t ) = τ π(t − ) E 2 ] ,τ −t ≤ t ≤ τ +t [1 − sin[ 0 0 kτ 2 2 2
0 -E
-T/2
t 0
t
0
T/2
-
τ τ τ 2 τ1 0 1 2 2 2 2 2
-2 0 2
题图 3-8
3-9 “升余弦滚降信号”的波形如题图 3-9-1 所示，它在 t 2 到 t3 时间范围内以升余弦的函数规 律滚降变化。设 t3 −
τ
2
=
τ
2
− t 2 = t0 ，则升余弦滚降信号的表示式可以写成
3-22 已知信号 f (t ) 的频谱为
1 [1 + cos(10 −3 ω )] , | ω |≤ 1000π rad s F (ω ) = 2 , 其它ω 0
现用冲激序列 δ T (t ) =
k = −∞
∑ δ (t − kT ) 对 f (t ) 进行理想抽样得抽样信号 f (t ) = f (t ) ⋅ δ
0
−ω 0
ω
0 ϕ 2 (ω )
ω0 π ωt 0
2
ω0
0
−ω 0
ω
0
（a）
青岛大学2015年硕士研究生入学考试初试试题考试科目：808英语综合
青岛大学2015年硕士研究生入学考试试题科目代码：808 科目名称：英语综合（共4页）请考生写明题号，将答案全部答在答题纸上，答在试卷上无效Part One Linguistics (50 points)I. Define the following terms briefly. (20 points)1. suprasegmental2. morpheme3. inflection4. immediate constituent analysis5. deep structure6. converse antonymy7. cooperative principle8. entailment9. interlanguage10. case grammarII. Answer ONE of the two essay questions below with at least 300 words. (30 points)1.How does Halliday relate the functions performed by language toits structures, or systems?2. Please give brief introductions to main branches of linguistics andgive a detailed description of one branch that you are interested in. Part Two Translation (50 points)I. Translate the following into Chinese. Your translation should both be anintelligibly fluent representation of the original text. （25 points）It is in the nature of things that the target text displays only the translator’s final decisions. Readers perceive an end-product, a result of a decision-making process; they do not have access to pathways leading to decisions, to the dilemmas to be resolved by the translator. What is available for scrutiny is the end-product, the result of translation practice rather than the practice itself. In other words, we are looking at translation as product instead of translating as process.The distinction is an important one, as Widdowson points out. Bellsuggests that the tendency to ignore the process involved in the act of translating lies behind the relative stagnation of translation studies in recent years. If we treat text merely as a self-contained and self-generating entity, instead of as a decision-making procedure and an instance of communication between language users, our understanding of the nature of translating will be impaired.II. Translate the following into English. Your translation should both be anintelligibly fluent representation of the original text. （25 points）我们以为所谓“直译”也者，带并非一定是“字对字”，一个不多，一个也不少。
信号与系统 第一章习题 王老师经典解法(青岛大学)小白发布
1-4 说明下列信号是周期信号还是非周期信号，若是周期信号，求其周期。 （1） f 1 (t ) = a sin(3t ) + b sin(8t ) ； （3） f 3 (t ) = a sin(3t )U (t ) ； （2） f 2 (t ) = a sin(π t ) + b sin(8t ) ； （4） f 4 (t ) = [ a sin(3t )] 。
（4） f 4 (t ) = sin(ωt ) ⋅ sin(8ωt ) ； （5） f 5 (t ) = [1 +
题图 1-7-1
1 sin(ωt )] ⋅ sin(8ωt ) 。 2
1-9 粗略绘出题图 1-9-1 所示波形的偶分量和奇分量。
1 0 -1 -1
f1 (t )
1
f 2 (t )
t
0 -1
∫
t
−∞
e(τ )dτ ；
d e(t ) ； dt 1 （4） r (t ) = e( t ) 。 4
（2） r (t ) = 3
1-14 有一线性时不变系统，当激励 e1 (t ) = U (t ) 时，响应 r1 (t ) = e
−2 t
cos(3t )U (t ) ，试求当
激励 e2 (t ) = δ (t ) 时，响应 r2 (t ) 的表达式（假定起始时刻系统无储能） 。
1-17 一具有两个初始条件 x1 (0) 、 x 2 (0) 的线性时不变系统，其激励为 e(t ) ，响应为 r (t ) 。 已知： （1）当 e(t ) = 0 ， x1 (0) = 5 ， x 2 (0) = 2 时， r (t ) = e (7t + 5) ， t > 0 ； （2）当 e(t ) = 0 ， x1 (0) = 1 ， x 2 (0) = 4 时， r (t ) = e (5t + 1) ， t > 0 ； （3）当 e(t ) =
青岛大学信号与系统考研真题2009—2011年
（15 分）15．电路如题图 15 所示， t 0 时开关 K 处于“1”的位置而且已经达 到稳态；当 t 0 时开关 K 由“1”转向“2”。
2 K i(t) R1 1
1
+
+
4V
2V
-
-
C 1F
L 1H 4
3
R2
2
题图 15
（1）试画出开关动作后的复频域等效电路； （2）求响应电流 i(t) 在 t 0 内的表达式。
青岛大学 2009 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 4 页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
Ⅰ、填空题（共 11 题，每空格 3 分，共 33 分）
1．对冲激偶信号 (t) ， (t)dt
，
(t
t0
)
f
(t)dt
。
2．时间函数 f (t) etu(t) 的傅里叶变换 F ( )
（3） 在题图 17 所示的解调过程中，试确定 A 、1 、2 之值，使得 y(t) g(t) 。
f (t)
A
y(t )
1 1
cos(2t)
题图 17
（20 分）18．已知离散时间系统的差分方程为 y(n) 0.81y(n 2) x(n) 0.81x(n 2)
（1）求系统函数 H (z) ，画出零、极点分布图； （2）求频率响应 H (e j ) ，粗略绘出幅频响应曲线，判断系统具有何种滤波特性； （3）求系统的单位样值响应 h(n) ，画出 h(n) 的波形； （4）以使用最少数量的单位延时器为条件，画出系统的仿真框图。
u(t)
则下列说法正确的是(
)。
信号与系统 第一章_绪论(青岛大学)小白发布
∫
∞
−∞ ∞
Sa (t )dt = π Sa 2 (t )dt = π
∫
−∞
另外一个类似的函数：
sin π t sinc( t ) = πt
§1.3 信号的运算
（一）对自变量进行的运算： 移位、反褶与尺度 对自变量进行的运算： 移位、 1. 移位： f (t ) → f (t ± t0 ) 移位：
t
t
t
sin (Ωt ) + sin (8 Ωt )
× sin ( Ωt ) sin (8 Ωt )
t
t
反相点
§1.4 阶跃信号与冲激信号 奇异信号： 奇异信号：
（一）单位斜变信号tu(t) （二）单位阶跃信号 u(t) （三）单位冲激信号δ (t) （四）冲激偶信号δ ' (t)
（一）单位斜变信号tu(t)
（3） cos(3n − )
当 当
2π
2π
π
ω0
为有理数时， 为周期序列； 为有理数时，sin(ω0n) 为周期序列； 为无理数时， 为非周期序列。 为无理数时，sin(ω0n) 为非周期序列。
2π 为无理数， 为无理数， 3
非周期序列
4
ω0
4．能量（有限）信号与功率（有限）信号 能量（有限）信号与功率（有限）
2.信号的传输、 2.信号的传输、交换和处理 信号的传输
信号传输（Transmission）
——古代烽火传送边疆警报 ——击鼓、信鸽、旗语等 击鼓、信鸽、 ——电信号传输（19世纪开始）： 电信号传输（ 世纪开始 世纪开始）：
1837年莫尔斯发明了电报 年莫尔斯发明了电报 1876年贝尔发明了电话 年
青岛大学2015年硕士研究生入学考试初试试题考试科目：827信号与系统
（1）零输入响应分量 yzi (n) ； （2）零状态响应分量 yzs (n) ； （3）全响应 y (n) ，并标示出自由响应、强迫响应分量。
3
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共
5
页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
T
0 2 2
T
t
图6
九、 （15 分）
+
因果离散时间系统如图 7 所示。 （1）选择合适的状态变量，列写 状态方程和输出方程 （化为矩阵方程形式） ； （2）列写出系统的差分方程。
x ( n)
∑ +
1 E
1/2 1/4
2
y ( n)
+
+ ∑ +
1 E
2
图7
十、 （10 分） 线性时不变连续时间系统的单位冲激响应 h(t ) 试求此系统的频率响应 H ( j) H ( j) e j( ) ？
g (t )
f (t )
低通滤波
cos(0t )
图3
12 ．序列 2n u (n ) 的双边 z 变换 X ( z )
2
，对应的收敛域
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共
5
页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效 为 。
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共
5
页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
一、填空题（每空格 2 分，共 30 分） 1．给定微分方程、起始状态、激励信号分别为
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并计算 t > 0 时的 i(t)。 2K
1Ω 1H
1
+
+
i(t )
1F
20V
10V
-
-
图4
四、（15 分） 描述某离散时间系统的差分方程为： y(n) y(n 1) 2y(n 2) x(n) 2x(n 2)
激励 x(n) u(n) ，初始条件为 y(1) 2 、 y(2) 1 ，求： 2
e(t)
-a0
图1
5．对单位冲激信号的导函数 (t) ，
(t
t0
)
f
(t)dt
。
n
6． (k) ________________，其中 δ(k)是单位冲激序列。
k
7．无失真传输网络的频率响应 H ( j) ________________，其中相位响 应() ________________。
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
为
。
二、（10 分）已知某信号 f(t)的拉普拉斯变换式 F(s)
3s
，
(s 2)(s 4)
求信号 f(t) 。
三、（15 分）电路如图 4 所示，t 0 开关 K 位于“1”且已达到稳态，t 0 时
刻，开关 K 自“1”转至“2”，试画出开关转到“2”后的复频域等效电路，
（1）零输入响应分量 yzi (n) ； （2）零状态响应分量 yzs (n) ；
（3）全响应 y(n) ，并标示出自由响应、强迫响应分量。
3
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 5 页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
一、选择题（每题 3 分，共 24 分）
x2(n)
3
1．离散序列 x1(n) u(n) u(n 2) ，x2 (n) 如
2
图 1 所示，则卷积和序列
1
y(n) x1(n) x2 (n) 的 最 大 取 值 发 生 在
01 2 3
n
（
）处。
Fs () F [ fs (t)] ，并画出频谱图。
六、（15 分）分别写出阶跃信号 u(t)、余弦信号 cos (ω0t)的傅里叶变换表达 式，并求出单边余弦信号 cos(ω0t)u(t)的傅里叶变换表达式。
七、（15 分）因果离散时间系统如图 5 所示
x(n)
∑
y(n) z 1
2 3
图5
（1）求系统函数 H (z) ，并画出系统的零、极点分布图；
信号 x(n) 。 八、（10 分）图 6 所示周期矩形波 p(t) ，其参数为T ， ， E 1。
3 求 p(t) 的指数形式傅里叶级数，并画出频谱图。
…
Tp(t)Βιβλιοθήκη E0 22图6
…
t T
九、（15 分）
因果离散时间系统如图 7 所示。 （1）选择合适的状态变量，列写
状态方程和输出方程 （化为矩阵方程形式）； （2）列写出系统的差分方程。
（2）求系统的单位冲激响应 h(n) ；
（3）若系统的零状态响应为 y(n) [4 (- 2)n +3 ( 1)n ]u(n) ，试求输入
3
2
4
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 5 页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
图1
A. n 0
B. n 1
C. n 2
D. n 3
2．以下描述系统的各方程中， x(n) 为激励， y(n) 为响应，则具有线性时
j3 2
z1 σ
0
j 3 2
图2
9. 一般的序列 x(n)可分解为共轭对称分量 xe(n)和共轭反对称分量 xo(n)的 叠加，则共轭对称分量 xe(n)= ________________。
10．某序列双边 z 变换的象函数是 X (z) 9z2 5-3z1 (0 z ) ，则原 序列 x(n)= ________________。
+
1
∑
+
E
x(n)
1/2
1/4
+
+ ∑
1
E
+
2
图7
y(n)
2
十、（10
分）线性时不变连续时间系统的单位冲激响应
h(t)
d dt
sin(ct ) t
，
试求此系统的频率响应 H ( j) H ( j) e j() ？
5
青岛大学 2016 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 5 页）
dt
r(0 ) 0 、 e(t) u(t) ，则 r(0 )
。
2．已知 x(n) h(n) u(n) u(n 4) ，则卷积和 y(n) x(n) h(n) 共有
个非零取值点。
3．积分 e jt d
。
4．图 1 所示系统的微分方程是________________。
r(t)
b1
1
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 5 页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
8. 若系统函数 H (s) 的零、极点分布如图 2 所示，其单位冲激响应的初值
h(0 ) 0.5 ，则 H (s)
。
jω
p1
-1 p2
11．图 3 所示以 f (t) 为输入、 g(t) 为输出的对调幅波进行解调的系统是：
（线性/非线性）、
（时变/时不变）系统。
f (t)
g(t)
低通滤波
cos(0t)
图3
12．序列 2n u (n )的双边 z 变换 X (z)
2
，对应的收敛域
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 5 页）
青岛大学 2015 年硕士研究生入学考试试题
科目代码： 827 科目名称： 信号与系统 （共 5 页）
请考生写明题号，将答案全部答在答题纸上，答在试卷上无效
一、填空题（每空格 2 分，共 30 分）
1．给定微分方程、起始状态、激励信号分别为 d r(t) r (t ) 2 d e (t )、
dt
五、（15 分）已知 f (t) Sa(2t) ，用T (t) ( t nT ) 对其进行理想抽样。 n
（ 1 ） 画 出 f (t) 的 频 谱 密 度 函 数 F() 的 图 形 ， 指 出 f (t) 的 最 高 频率 fm ? (Hz) ；
（2）怎样选择抽样频率 fs ，才可以做到无失真抽样？ （ 3 ） 若 取 fs 6 fm ， 求 抽 样 信 号 fs (t) f (t) T (t) 的 频 谱 密 度 函 数