Radio Frequency Integrated Circuit Design - Webs

Voltage-Controlled Oscillators
Figure 8.53 Resonator current for the VCO with ACC (reduced phase margin).
Figure 8.54 Resonator voltage for the VCO with AAC loop.
8.20 Other Oscillators
Although we have stressed LC-based VCOs in this chapter as the most common
RF oscillators due to their excellent phase noise, there are many other ways to
build a circuit that generates harmonic waveforms. One example is a voltagecontrolled,
emitter-coupled multivibrator oscillator as shown in Figure 8.56.
Q 1 and Q 2 alternately turn on, and I1 goes through the capacitor C,
causing a ramp of voltage until the other transistor is turned on. First note that
Q 5 and Q 6 are always on, each sinking current I1. Also note that Q 3 and Q 4
are always on due to Ix and Iy , and thus v b2 is always one diode drop less than
vc1, and v b1 is always one diode drop lower than vc2. In the waveforms shown
in Figure 8.56, we have assumed that a diode or base-emitter junction, when
forward biased, has a voltage drop of V BE(ON) = 0.8V. Thus, if Q 1 switches
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