Browse Prior Art Database

Preamplifier

IP.com Disclosure Number: IPCOM000084012D
Original Publication Date: 1975-Sep-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Frankeny, RF: AUTHOR [+3]

Abstract

A common record/play preamplifier is incorporated into a battery operated recorder, for stabilizing gain and bias level and rejecting power supply noise.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 100% of the total text.

Page 1 of 2

Preamplifier

A common record/play preamplifier is incorporated into a battery operated recorder, for stabilizing gain and bias level and rejecting power supply noise.

Transistors Q2 and Q3 form a low-noise input stage for the preamplifier A. To minimize the amplifier noise, the bias current in Q2 must be maintained at its optimum level during variations in the supply voltage. Q2 and Q3 form a feedback amplifier having a closed-loop gain, which is a function of the individual transistor gains and the ratio of R6 to R5. The gain is a function of Q2 and Q3 bias currents and must be stabilized against supply variations. If I(C3) is made approximately equal to I(C2) by design, the bias current in Q2 is independent of the supply voltage.

With the current I(C2) being low, the voltage on the base of Q2 is very nearly equal to the base-to-emitter voltage of Q2. Since only the base current flows through R1, V(n) is approximately equal to the voltage on the base of Q2. The output of the amplifier A is thus biased at (R11 + R2/R11)V(BE), independent of +B.

Power supply noise rejection is achieved by R7 and Cl forming a low-pass filter to filter +B variations, and Q2 and Q3 providing power supply noise rejection by design. Power supply noise is common to the emitter of Q2 and the base of Q3.

1

Page 2 of 2

2

[This page contains 2 pictures or other non-text objects]