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Ideal Frequency to Voltage Filter

IP.com Disclosure Number: IPCOM000050787D
Original Publication Date: 1982-Dec-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 35K

Publishing Venue

IBM

Related People

Bustamante, CM: AUTHOR [+2]

Abstract

The circuit shown in Fig. 1 acts as an ideal filter in frequency to voltage conversion applications. It contains a sawtooth and analog memory circuit, shown in Fig. 4, which under certain conditions generates sawtooth oscillations and, upon being pulsed by comparator circuit level existing at the time of the comparator pulse.

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Ideal Frequency to Voltage Filter

The circuit shown in Fig. 1 acts as an ideal filter in frequency to voltage conversion applications. It contains a sawtooth and analog memory circuit, shown in Fig. 4, which under certain conditions generates sawtooth oscillations and, upon being pulsed by comparator circuit level existing at the time of the comparator pulse.

When the output of comparator 10 is positive, sawtooth and analog memory circuit 12 applies a sawtooth waveform to VCO (voltage-controlled oscillator) circuit 14 which sweeps the output of circuit 14 through a predetermined frequency domain bounded by known frequencies f1 and f2 (refer to Fig. 2). The VCO output and "variable frequency input" 16 are applied to doubly balanced modulator 18. If the frequency of input 1-6 is in the band associated with the VCO output, at some point in time (19) the two signals will coincide, causing the comparator to switch. The resulting negative pulse transition of comparator 10 triggers circuit 12 to hold the immediate voltage condition of its sawtooth output. This stabilizes the VCO 14 output at the input frequency and causes the output of the comparator to remain low. The output of comparator 10 is applied through delay circuit 20 to "good data" gating port 22 and the output of circuit 12 is applied to voltage indicating port 24. Accordingly, at a predetermined time after the negative transition at the output of comparator 10, an enabling pulse level appears at port 22, permitting external apparatus to sample the voltage then presented at port 24.

For each frequency in the range fl to f2, there is a unique corresponding voltage condition on the ramp output of circuit 12. Hence, the circuit of Fig. 1 acts as an ideal frequency to voltage converter. The circuits shown in Fig. 1 require fewer than 60 active transistor elements, and, when implemented by integrated circuit techniques, can easily fit on a single small-scale integrated circuit chip. Comparable contemporary circuits which employ sophisticated filtering techniques w...