ML1490 Ver la hoja de datos (PDF) - LANSDALE Semiconductor Inc.

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ML1490

RF/IF/Audio Amplifier Wideband Amplifier With AGC

LANSDALE Semiconductor Inc. 

ML1490

LANSDALE Semiconductor, Inc.

DESCRIPTION OF SPEECH COMPRESSOR

The amplifier drives the base of a PNP transistor operating

common–emitter with a voltage gain of approximately 20. The

control R1 varies the quiescent Q point of this transistor so

that varying amounts of signal exceed the level Vr. Diode D1

rectifies the positive peaks of Q1's output only when these

peaks are greater than Vr ≈ 7.0 V. The resulting output is fil-

tered by Cx, Rx.

Rx controls the charging time constant or attack time. Cx is

involved in both charge and discharge. R2 (the 150 kΩ and

input resistance of the emitter–follower Q2) controls the decay

time. Making the decay long and attack short is accomplished

by making Rx small and R2 large. (A Darlington emitter–fol-

lower may be needed if extremely slow decay times are

required.)

The emitter–follower Q2 drives the AGC Pin 5 of the

ML1490PP and reduces the gain. R3 controls the slope of sig-

nal compression.

Table 1. Distortion versus Frequency

Frequency

100 Hz

Distortion

10 mV ei

3.5%

100 mV ei

12%

Distortion

10 mV ei

15%

100 mV ei

27%

300 Hz

2%

10%

6%

20%

1.0 kHz

1.5%

8%

3%

9%

10 kHz

1.5%

8%

1%

3%

100 kHz

1.5%

8%

1%

3%

Notes 1 and 2

Notes 3 and 4

Notes:

(1) Decay = 300 ms

Attack = 20 ms

(2) Cx = 7.5 µF

Rx = 0 (Short)

(3) Decay = 20 ms

Attack = 3.0 ms

(4) Cx = 0.68 µF

Rx = 1.5 kΩ

Figure 24. Speech Compressor

+12 V

25 µF

0.001

1.0 k

1.0 k

15 µF

Input

2

5

1

4 ML1490

8

6

3

10 µF

10 µF

15 µF

7

+12 V +12 V

R3

15 k

+12 V

Q2

2N3904

220 2.2 k

R2

Q1

2N3906

Vr

Rx D1

33 k

4.7 k 150 k

Cx

6.8 k

R1

100 k

Output

Page 7 of 8

www.lansdale.com

Issue A

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