Document No. 510 - 78 - 06

GENNUM

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Programmable Analog

Signal Processor

GP520A - DATA SHEET

Principle features of the preamp are the input impedance

100 k

Ω and a gain of 14 dB.

The programmable filter block is composed of a low pass

and high pass filter which generates a range of high and

low pass corner frequencies. Although the control current

to this block varies linearly, linear to logarithmic conversion

is performed internally in order to adjust the corner frequencies

logarithmically. Both filters feature a 12 dB/octave rolloff

and unity gain.

The filters are followed by an AGC block. Up to 35 dB of

adjustable gain is provided as well as programmable

threshold and release time. The attack time of the AGC

block remains fixed and is independent of the release

time. The output current is driven into the preamp of the

clipper, thus, the AGC converts a voltage input into a

current output and is therefore, a transconductance block.

The next stage is an electronic MPO control peak “clipper”

providing electronic clipping of the signal and setting of

the maximum output level. The clipper output is also a

transconductance block and drives a 40 k

Ω resistor (R

OUT 8

)

tied to the supply.

The input of the final stage is an inverting operational

amplifier. A feedback resistance of 240 k

Ω is provided

internally and this final stage is thus configured as a

voltage drive output stage. The DC bias current through

the receiver is also programmable.

FEATURES

• programmable parameters

- gain

- low pass filter

- high pass filter

- AGC threshold

- release time

- MPO

- receiver bias voltage

• on-chip voltage regulator

• typical gain 60 dB

• voltage drive output stage

• telecoil preamp

FUNCTIONAL BLOCK DIAGRAM

FULL WAVE

RECTIFIER

AVERAGING

CIRCUIT

THRESHOLD

AGC

Vcc

RF

LIN/LOG

CONVERTER

LIN/LOG

CONVERTER

LIN/LOG

CONVERTER

R

2R

HP

FILTER

+

-

PREAMP

+

-

40K

R

IN14

10K

VOLTAGE

REGULATOR

R

R

14

13

9

18

15

19

22

24

26

27

1

3

5

7

8

10

11

17

4

23

2

25

16

21

20

6

GND

D

OUT

D

IN

C

OUT

B

OUT

B

IN

DELTA

OUT

C

AGC

RECT.

IN

BUFFER

OUT

BUFFER

IN

+

-

LP

FILTER

LPFB

HP

HPFB

A

OUT

V

CC

V

REG

A

IN

OUTPUT

-

+

12

P GND

C

COMP

31

30

C

CLIP

29

28

50k

VC AMP

CLIPPER

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

STANDARD PACKAGING

• Chip (136 x 110 mils)

Au Bump

CIRCUIT DESCRIPTION

The GP520A is a programmable analog signal path IC

designed for use in hearing instruments. The GP520A’s

programmable parameters are adjusted by external

programming currents, such as generated by the GP521.

The GP520A provides a 2.5

µA reference current for use by

the GP521. Sixteen settings are possible in the GP521,

allowing the Programmable Current Sink (PCS) to sink

between 0 and 1.875 x I

The GP520A is composed of five functional blocks. The

input preamp, a filter block, the AGC block, MPO clipper

and the output stage.

Revision Date: May 1998

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

Web Site: www.gennum.com

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