Circuit doubles frequency-deviation ratio of given VCO. Control voltage of MC1658 VCO, with range of 0 to -2 V, is attenuated and then applied to AM685 opamp comparator. When control voltage reaches an extreme and crosses over amplifier's reference voltage, detector switches to opposite state. Circuit output is thus either that of VCO or VCO divided by 2. Article describes op-eration in detaiL-E. Kane, Expander Doubles VCO Frequency Deviation, EDN Magazine, Jan. 20, 1977, p 94.
The MC1658 is a voltagecontrolled multivibrator which provides appropriate level shifting to produce an output compatible with MECL III and MECL 10,000 logic levels. Frequency control is accomplished through the use of voltagevariable current sources which control the slew rate of a single external capacitor.
The bias filter may be used to help eliminate ripple on the output voltage levels at high frequencies and the input filter may be used to decouple noise from the analog input signal.
Required Field 
