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Variable Gain Amplifier for Light Sensitive Diode

IP.com Disclosure Number: IPCOM000092926D
Original Publication Date: 1967-Mar-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Dryer, JE: AUTHOR

Abstract

The gain of amplifier A can be varied as a function of amplitude by changing the amount of feedback for the amplifier. With no light L impinging on diode DL, diodes D1 and D2 are forward biased by the current established between sources +V and -V. The potential of node B will not vary as a function of the output and therefore there is no feedback around A. However, as light L impinging on DL increases, D1 and D2 become backbiased allowing the potential at node B to vary as a function of the output thus providing feedback around A. For small signals the gain of A is large since there is no feedback around it. However, as the signal is increased and the feedback becomes effective, the gain of A is reduced to provide an amplifier with two levels of gain.

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Variable Gain Amplifier for Light Sensitive Diode

The gain of amplifier A can be varied as a function of amplitude by changing the amount of feedback for the amplifier. With no light L impinging on diode DL, diodes D1 and D2 are forward biased by the current established between sources +V and -V. The potential of node B will not vary as a function of the output and therefore there is no feedback around A. However, as light L impinging on DL increases, D1 and D2 become backbiased allowing the potential at node B to vary as a function of the output thus providing feedback around A. For small signals the gain of A is large since there is no feedback around it. However, as the signal is increased and the feedback becomes effective, the gain of A is reduced to provide an amplifier with two levels of gain.

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