Synthesised reactance crystal VCO - gives positive and negative deviation with DC to HF bandwidth using crystal current sensing phase shift and multiplier loop

摘要

The oscillator consists of a synthetic reactance varied linearly with a modulating voltage connected in series with a quartz crystal (12) oscillator. It consists of a loop in series generating a voltage proportional to the current through the crystal a phase shift (16) and a four quadrant multiplier (18) having the modulation control voltage as one input. The current sensing is performed by a differential input amplifier (15) connected across a series damping resistor (14) with a further amplifier (11) between the multiplier and the crystal. This has a differential output and is connected across the crystal with an intermediate capacitor (13) which compensates for the inter electrode capacitance of the crystal. The incoming control voltage is filtered by an integrator (20) to remove components over 100 KHz. The output of the crystal oscillator is fed to a phase discriminator (4) along with the output of a VCO (1) after division (3).