电子电路复习资料

1.Materials in nature are categorized into conductors, insulators and semiconductors according to t heir electric al conductivity.

2. Intrinsic semiconductor refers to pure semi conductor crystal.

3.An N type mate rial is created by doping impurity elements that have five valence electrons( pentavalent ),such as phosphorus, antimony锑（Sb）, and arsenic砷, to the intrinsic semiconductor.

4.A P type material is created by doping impurity elements that have three valence elect rons(trivalent ),such as boron, gallium, and indium ,to the intrinsic semiconductor.

5.The V-I charact eristic of a diode can be shown the oretically by the Shockl y equation IS is the reverse saturation current; .u D is the external voltage across the diode;, VT=kT/q is called thermal voltage

6. When PN junction is forward biased, the depletion region is narrowed.

7. Different terminals should be doped in different methods .The emitte r layer should be heavily doped, the base lightly doped, and the collector also lightly doped. The base layer should be very thin and the width of collector area should be large. This kind of structure is the basic condition for a BJT having amplific ation ability.

8. BJT has t hree operation modes, correspondi ng t o three regions of BJT operating curves, they are linear-region operation, cutoff–region operation and saturation-region operation.

9.Operation conditions in the cutoff, saturation, and linear regions of the BJT characteristics a re provided as follows:

(1) Linear-region operation

Base-Emitte r junction forward-biased

Base-Collector junction reverse-biased

(2)Cutoff –region operation

Base-Emitte r junction reverse-biased

Base-Collector junction reverse-biased

(3) Saturation-region operation

Base-Emitte r junction forward-biased

Base-Collector junction forward-biased

10.There are Three equivalent models commonly used in the sm all signal AC analysis of transistor networks:the re model, the h ybrid πmodel and t he hybrid equivalent model.

11. There are thre e modes of BJT amplifi er: common-e mitte r configuration, common-collector configuration and common-base configuration.

12.FET transistor is the semi conductor controlled by the electric field.

13.There are t wo types of FET s: the junction field-e ffe ct transistor (JFET) and the metal-oxide-se miconductor field-e ffe ct transistor (MOS FET).

14.The relationship between ID and UGS is defined by Shockley equation ID=IDSS(1-UGS/V P)²

15.A current mirror circuit is composed by basic amplifiers and can provide constant c urrent.

16.The structure of t he current mirror circuit require that the transistors used have identical base-emitter voltage drops and identical values of beta.

17.The main featu re of differential a mplifie r is that it has the very large gain for the differential-mode signals as compa red to the very slight gain for common-mode signals.

18.The basic differential ampli fier circuit is has two separate inputs and out puts and symmetric structure.

19.After obtaining t he differential-model voltage gain Aud and the common-mode voltage gain Auc ,the CMRR is defined as KCMRR=Aud/Auc

20.Several basic amplifiers are often combined as multistage amplifie r to mee t the actual application requirements.

21.The connection mode between two stages is called the couple method.

22.For multistage amplifier, the basic coupling modes between stages include the RC-coupling mode the direct connection coupling mode(also named as cascade connection) and the transformer coupling mode.

23.The merits of RC-coupli ng mode are the independent quiescent operation points of the form and latter stages.

24.But t here are also shortcomings for the RC-coupling mode. the RC-coupling mode multistage amplifiers can hardly used in IC.

25.The merits of di rect connection coupling mode is the amplifying ability for both AC input signals and the DC signals or signals varying slowl y.

25.The quiescent operation point of the direct connection coupling mode multistage amplifier will be unstable.

26.For an n-stage multistage amplifier, the total voltage gain is Au=Au1.Au2.Au3……Aun

27.The multistage ampli fiers can provide better ampli fying ability and fulfill the merits of the basic amplifier configurations.

28.If the effect of the capacitive ele ments can be ignored in some bandwidth and the focus i s on resistive elements, the amplifie r gain c an be constant, which is ca lled the mid-frequency range. 29.The fe ature that ampli fier gain will change with the diffe rent frequency is called frequency response.

30.There fore, the ci rcuit passes the low frequency signal and no output for the hi gh frequency signal, whic h is called low-pass circuit.

31.There fore, the circuit passes the high frequency signal and no output for the low frequency signal., which is called high-pass circuit.

32.If the frequency response is plotted by logarithmic scale, the plot is called Bode plot.

33.For a 10:1 change in frequency, equivalent to one decade, there is a20dB change in the ratio.

34.The primary reason for the drop in gain at the low frequency is the increasing reactance of Cs, CE and Cc.

35.The large c apacitive el ements determine the low-cutoff frequency. Whereas the s malle r pa rasitic capacitors det ermine the high-cutoff frequency.

36.The frequency at which the gain drops to 70.7% of the midband value are called the cutoff or half-powe r frequency. 37.However, someti mes the output signal can affect the input signal reversely, which is termed as feedback.

37.The feedback si gnal is in opposite polarity t o t he origi nal input signal causing the net input signal be reduced compared to the original input signal.

38.Negative series feedback increas es input resistance to (1+AF)ti mes the open-loop input resistance.

39.negative parallel feedback reduces input resistance to one (1+AF)th of the open-loop input resistance.

40.negative voltage feedback reduces the output resistance of an amplifie r to one (1+AF)th of the open-loop output resistance. 41.the negative current feedback increases the output resistance of an ampli fier to(1+AF)ti mes of the open-loop output resistance.

42.negative feedback reduces the gain of the closed-loop amplifie r to one (1+AF)th of that of the open-loop gain.

43.the bandwidth of the closed-loop amplifier is increased to (1+AF)ti mes of the bandwidth of the open loop amplifier.

44.class A:the output signal varies for a full 360 of the cycle.

45.class B:the class B power amplifi er provides an output signal varying over one-half the input signal cycle or 180 of signal. 46.most class A circuits will provide efficiencies o f less than 25% .t he efficiency can be improved using transformer coupled class A amplifier and can be up to 50%.

47.for the class B amplifiers, there is no bias, t o obtain output for the full cycle of signal, it is necessa ry to use two complementary transistors.

48.class A:maximu m efficiency of 25%(without transformer) and 50%(transforme r).

49.class B: maximum efficiency of 78.5%.

There are Thre e equivalent models commonly used in the small signal AC analysis of transistor networks: the re model, the hybri d πmodel and the hybrid equi valent model.

There a re thre e modes of BJT a mplifie r: common-e mitte r configuration, common-collector configuration and common-base configuration.

47classB：The class B power amplified provides an output signal varying over one-half the input signal cycle or 180 of signal 48. Therefore, most Class A circuits will provide efficienci es of less than 25%. The effi ciency can be improved using transformer-coupled Class A amplifier and can be up t o 50%.

49 For the Class B amplifiers .ther e is no bias.

50 T o obtain output for the full cycle of signal, it is necessary to use two complementary transistors

51 An i dea op-amp has the follows characteristics

(1) infinite open-loop gain for the differential signal Aud=∞.

(2) infinite input resistance as Rid=∞

(3) Ze ro output resistance as R0=0

(4) infinite bandwidth

(5) infinite common mode rejection ratio as Kc mr=∞

52 “Virtue short” indicates the conditi on th at the two i nput terminals a re seen to have the same potential

53 “Virtue open” indicate the condition that the two input terminals a re seen to be open

54 If feedback element is capacitor. An integrator can be constructed

55 IF the element on input branch is capacitor . An differentiator can be constructed

56 Another type of comparators used with positive feedback. T e rmed as Schmitt trigger, can overcome the problem by introducing two thresholds.

57 Operational amplifie r is constructed by input stage, mid dle amplific ation stage, output stage and bias circuits

58 An op-amp is connected with strong negative feedback to ensure its operation in the li near region

59 Comparators operate in the nonlinear region, where the output i s either high or low

60 Comparators are connected in open-loop or with positive feedback