MC1490 Motorola, MC1490 Datasheet - Page 7

• Manufacturer Part Number: MC1490
• Description: WIDEBAND AMPLIFIER WITH AGC
• Manufacturer: Motorola

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 V r . Diode
D1 rectifies the positive peaks of Q1’s output only when these
peaks are greater than V r
filtered by C x , R x .
involved in both charge and discharge. R2 (the 150 k
input resistance of the emitter–follower Q2) controls the
decay time. Making the decay long and attack short is
accomplished by making R x small and R2 large. (A
Darlington emitter–follower may be needed if extremely slow
decay times are required.)
MC1490P and reduces the gain. R3 controls the slope of
signal compression.
MOTOROLA ANALOG IC DEVICE DATA
The amplifier drives the base of a PNP transistor operating
R x controls the charging time constant or attack time. C x is
The emitter–follower Q2 drives the AGC Pin 5 of the
DESCRIPTION OF SPEECH COMPRESSOR
Input
]
7.0 V. The resulting output is
R3
15 k
15 F
2N3904
4.7 k
Q2
Figure 24. Speech Compressor
+12 V
15 F
150 k
+12 V
5
4
6
and
MC1490
MC1490P
2
R2
7
C x
25 F
0.001
1.0 k
1.0 k
R x
1
Notes:
Frequency
Frequency
100 Hz
300 Hz
1.0 kHz
10 kHz
100 kHz
2N3906
3
6.8 k
D1
220
8
Q1
+12 V
(1) Decay = 300 ms
(2) C x = 7.5 F
Table 1. Distortion versus Frequency
100 k
2.2 k
33 k
R1
Attack = 20 ms
R x = 0 (Short)
10 mV e i
+12 V
3.5%
1.5%
1.5%
1.5%
10 F
2%
10 F
Notes 1 and 2
Distortion
V r
100 mV e i
12%
10%
8%
8%
8%
Output
(3) Decay = 20 ms
(4) C x = 0.68 F
10 mV e i
15%
6%
3%
1%
1%
Attack = 3.0 ms
R x = 1.5 k
Notes 3 and 4
Distortion
100 mV e i
27%
20%
9%
3%
3%
7