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# Differentiator and Amplifier

IP.com Disclosure Number: IPCOM000091686D
Original Publication Date: 1968-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 36K

IBM

## Related People

Boggs, BR: AUTHOR [+3]

## Abstract

This is a differentiator and amplifier circuit for a differential input signal which provides a differential output signal which is the amplified derivative of the input differential signal. The capacitor C1 forming the differentiating circuit has both differential inputs applied thereto, thereby eliminating any charge buildup.

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Differentiator and Amplifier

This is a differentiator and amplifier circuit for a differential input signal which provides a differential output signal which is the amplified derivative of the input differential signal. The capacitor C1 forming the differentiating circuit has both differential inputs applied thereto, thereby eliminating any charge buildup.

The differential input signal is applied at terminals 10 and 11 to the bases of transistors T12 and T13 connected as emitter-followers. The output signals of T12 and T13 are applied respectively to the bases of transistors T14 and T15. The sum of resistors R1 + R2 + R3 is chosen to be several times the impedance value of capacitor C1 at the operating frequency. This forces emitter current i(e) of T14 and T15 to be approximately equal to capacitor current i(c). The impedance of C1 is chosen to be several times the magnitude of the sum of the h(ib) parameters of T14 and T15 thus forcing the input voltage V to be impressed across C1. Thus, current through the capacitor is i(c) = C1 dV/dt. Since collector current i(col) is approximately equal to the emitter current which is approximately equal to the current through C1, the voltage across the collectors Vc is Vc = (R4 + R5) i(col) = (R1 + R2) C1 d V/dt.

Thus, the collector voltage is the derivative of the input voltage times a constant >(R4 + R5) C1|. The output at terminals 16 and 17 can then be directly coupled to a second stage differential amplifier for furth...