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Quartz_stabilized_bridge_oscillator

2016-05-15 14:59  
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Quartz_stabilized_bridge_oscillator
Figure 4-24 shows a bridge-based oscillator, where one leg of the bridge is replaced with a resonant element. Figure 4-25 shows the waveforms. With the crystal removed, the circuit is a basic non-inverting gain-of-two amplifier with grounded input. Inserting the crystal closes a positive-feedback path at the crystal resonant frequency. The amplifier output (trace A, Fig. 4-25) swings in an attempt to maintain input balance. Excessive circuit gain prevents linear operation, and oscillations start when the amplifier repeatedly overshoots in an attempt to null the bridge. The high Q of the crystal is evident in the filtered waveform (trace B) at the amplifier positive input. LINEAR TECHNOLOGY APPLICATION NOTE 43, P. 27.