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System For Varying Oscillator Frequency

IP.com Disclosure Number: IPCOM000096363D
Original Publication Date: 1963-Apr-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Abstract

In a particular character recognition system, it is necessary to vary the frequency of an oscillator in accordance with document speed variations.

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System For Varying Oscillator Frequency

In a particular character recognition system, it is necessary to vary the frequency of an oscillator in accordance with document speed variations.

The frequency of the oscillator is varied by varying the capacitance of its tuning circuit. This is accomplished by means of the Miller effect. he Miller effect depends upon an amplifier to magnify the capacitance of a capacitor. The magnitude of the apparent capacitance is a function of the gain of the amplifier.

Document transport shaft 10 is mechanically connected to the shaft of electrical tachometer 15. The output of 15 is an AC electrical current whose magnitude is directly proportional to the transport or document speed. The output of 15 is connected to an amplifier and rectifier 20. This amplifies the AC signal and rectifies it to DC current. The output of 20 is connected to the input of amplifier 25 to forwardly biased diode D and to resistor R.

The amplifier 25, diode D and resistor R form a Miller amplifier. The output of amplifier is connected to capacitor C which, in turn, is connected in the tuning circuit of oscillator 30.

The small signal resistance of diode D is inversely proportional to the DC current passing through it. Hence, as the current output of tachometer 15 varies, the resistance of diode D varies. This resistance of diode D is r. The overall gain of the Miller amplifier is proportional tor/(R+r).

By this arrangement, if transport shaft 10 increases in...