Document No. 510 - 12 - 08

Class A Amplifier with

3 Gain Blocks & Schottky Diodes

LS509 DATA SHEET

BLOCK DIAGRAM

DESCRIPTION

The LS509 is a Class A amplifier utilizing Gennum’s proprietary

low voltage JFET technology. It consists of two single-

ended, low noise inverting gain blocks, a Class A output

stage, an on-chip microphone decoupling resistor and a

pair of Schottky diodes for symmetrical peak clipping.

Blocks A and B typically have an open loop voltage gain of

56 dB, with the closed loop gain set by the ratio of the

feedback resistor to the source impedance. It is recommended

that the maximum closed loop gain be 20 dB lower than the

open loop gain. All blocks of the device are internally bias

compensated, preventing any DC current flow via external

feedback resistors. Without this compensation, audible

scratchiness would be present during changes in volume

control settings.

The output stage of the LS509 is a Class A current drive.

It has a fixed reference voltage of typically 29 mV at pin 2

of the device. The current that flows in the transducer is the

ratio of the 29 mV reference voltage and the on-chip

emitter resistor (R

E

).

To increase the bias current in the

transducer, simply place an external RE resistor from pin

2 to ground, thereby decreasing the equivalent emitter

resistance and increasing the current.

The LS509 also contains a pair of Schottky diodes in the

feedback configuration of the output stage, which provides

approximately 12 dB of MPO control.

• 140

µA typical current drain

•

low noise and distortion

• 1.0 to 5 VDC operating range

•

independent preamplifier

•

2 DC coupled stages

•

class A output stage

•

variable transducer current

•

Schottky diodes for MPO control

•

4 k

Ω microphone decoupling resistor

FEATURES

STANDARD PACKAGING

• 10 pin PLID

®

• 10 pin SLT

• Chip (61 x 55 mils)

7

3

2

4

5

6

1

10

9

8

21k

C

-

B

-

A I/P

A O/P

B I/P

B O/P

GND

MPO

C O/P

All resistors in ohms, all capacitors in farads unless otherwise stated

Revision Date: January 2001

GENNUM CORPORATION P.O. Box 489, Stn. A, Burlington, Ontario, Canada L7R 3Y3 tel. +1 (905) 632-2996

Web Site: www.gennum.com

E-mail: hipinfo@gennum.com