Browse Prior Art Database

Wide Range Modulator

IP.com Disclosure Number: IPCOM000098776D
Original Publication Date: 1959-Dec-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

Laczko, L: AUTHOR

Abstract

The provision of four identical voltage variable capacitors C(1), C(2), C(3) and C(4), as the effective elements in a balanced bridge modulator circuit, results in a modulator which has a wide frequency response. It is capable of handling d.c. input signals E(I) as well as a. c. signals E(I) up to several megacycles. In addition, the modulator has a low noise level and is sensitive enough to handle low level signals E(I) such as, for example, 20 millivolts.

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Wide Range Modulator

The provision of four identical voltage variable capacitors C(1), C(2), C(3) and C(4), as the effective elements in a balanced bridge modulator circuit, results in a modulator which has a wide frequency response. It is capable of handling d.c. input signals E(I) as well as a. c. signals E(I) up to several megacycles. In addition, the modulator has a low noise level and is sensitive enough to handle low level signals E(I) such as, for example, 20 millivolts.

A signal E(I) is applied across C(1) at bridge terminals 1 and 2. An alternating signal for modulation of E(I) is provided from a generator G across the bridge terminals 2 and 4. The generator signal is prevented from feeding back to the input by the filtering action of R(1), R(2) and C(5).

If no signal E(I) is present, the bridge is balanced and no signal is provided on the line 5 to the a.c. amplifier A.

When a signal E(I) is applied, the capacitance, in micro microfarads, of C(1) changes in a linear manner with respect to E(I) as shown in the graph. The bridge becomes unbalanced and an alternating signal which is a composite of the signal from G and E(I) is then established on line 5 to A for amplification. A synchronous diode D is provided to produce a rectified output E(O). The voltage on one side of the diode D fluctuates in synchronism with and under control of the generator G, on line 6, so that E(O) follows E(I) in a positive as well as a negative direction.

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