高频第四章

Fig.4.9 Serial crystal oscillator Crystal oscillates at its serial frequency and is regarded approximately as short.
4.4.3 Discrete Pierce oscillator
Fig.4.10 Discrete Pierce oscillator
3. Frequency Stability 3.1 Representation of frequency stability Maximum difference of frequency in a give term Sf = Desired frequency 3.2 Factors with stability
5. IC waveform generators
Fig.4.11 IC waveform generator •An oscillator •A wave shaper •An optional AM modulator •Output buffer amplifier
Fig.4.12 Monolithic voltage-controlled oscillator
Balanced oscillation
Aol 1 A 2n
2. LC Oscillators
2.1 Three-pointed oscillator
Fig.4.2 Three-pointed LC oscillator
Generally, it is easy for oscillation circuit to meet prerequisite of amplitude ( fulfilled( A
•Changes in inductance, capacitance and resistance.
•Changes in the quiescent operating point of transistor. •DC change resulted form AC ripples.
4. Crystal oscillators 4.1 Piezoelectric effect Oscillating mechanical stresses applied cross a crystal lattice structure generates electrical oscillation, and vice versa. 4.2 Crystal cuts The natural resonant frequency is determined by the type, length and thickness of a cut and the mode of vibration.
Aol 1).Therefore, so long as prerequisite of phase is
ol
2n
), it is sure that the circuit would start and
maintain the oscillation. Phase prerequisite of oscillation is equal to that Vf is same Vi in phase. For Vf and Vi being same phase, it must be met that X1 and X2 is same reactivity, while X3 is inverse reactivity with them.
Q 10 ~ 10
4
5
Fig.4.6 Equivalent circuit of crystal
Fig.4.7 Impedance and reactance of crystal
4.4 Crystal oscillator
4.4.1 Parallel crystal oscillator (Discrete Pierce oscillator)
CHAPPTER 4
1.Feedback Oscillators
1.1Requirements • Amplification • Positive feedback
Signal Generation
• Frequency-determining components • Power supply
1.2 Prerequisite for oscillation
2.2 Hartley oscillator
Fig.4.3 Hartley oscillator
f0
1 2 LC
L L1a L1b , C C1
2.3 Colpitts oscillator
Fig.4.4 Colpitts oscillator
f0
1 2 LC
C1aC1b L L1 , C C1a C1b
Fig.4.1 Block diagram of oscillator
Vo AolBaidu Nhomakorabeai
Vf Vo Aol Vi
Vf Vi Aol 1
Aol 1 A 2n
Starting oscillation
Aol 1 A 2n
Fig.4.8 Parallel crystal oscillator Crystal oscillates between its series frequency and parallel frequency, used as an inductor.
4.4.2 Serial crystal oscillator
Fig.4.5 Quartz crystal: (a)basic crystal structure; (b)crystal axes;(c)crystal cuts;(d)crystal mountings
4.3 Crystal equivalent circuit
L: The mass of the crystal in vibration, 0.1H~100H. R: The mechanical friction loss.→0. C1: The mechanical compliance of the crystal, ≤1pF. C2: The actual capacitance between the electrodes of the crystal, 4~40pF.