OP470ARCMDA AD [Analog Devices], OP470ARCMDA Datasheet - Page 14

• Manufacturer Part Number: OP470ARCMDA
• Description: Very Low Noise Quad Operational Amplifier
• Manufacturer: AD [Analog Devices]

OP470
SQUELCH AMPLIFIER
The circuit of Figure 17 is a simple squelch amplifier that uses a
FET switch to cut off the output when the input signal falls
below a preset limit.
The input signal is sampled by a peak detector with a time
constant set by C1 and R6. When the output of the peak detector
(Vp), falls below the threshold voltage, (VTH), set by R8, the
comparator formed by op amp C switches from V– to V+. This
drives the gate of the N-channel FET high, turning it ON, re-
ducing the gain of the inverting amplifier formed by op amp A
to zero.
V
IN
2k
2k
R1
R3
100k
Figure 17. Squelch Amplifier
R5
= 1 SECOND
1/4
OP470E
A
1/4
OP470E
B
10k
10k
R2
R4
2N5434
1N4148
D1
V
OUT
– –5V
C1
1 F
V+
1N4148
IN
D2
R6
1M
10k
R6
R7
10k
1/4
OP470E
C
10M
10 F
+
R4
C2
–14–
FIVE-BAND LOW-NOISE STEREO GRAPHIC EQUALIZER
The graphic equalizer circuit shown in Figure 18 provides 15 dB
of boost or cut over a 5-band range. Signal-to-noise ratio over a
20 kHz bandwidth is better than 100 dB referred to a 3 V rms
input. Larger inductors can be replaced by active inductors but
this reduces the signal-to-noise ratio.
V
IN
Figure 18. Five-Band Low Noise Graphic Equalizer
0.47 F
47k
C1
R1
680
680
680
680
680
R11
R3
R5
R7
R9
TANTALUM
TANTALUM
TANTALUM
TANTALUM
TANTALUM
1/4
OP470E
0.022 F
0.047 F
0.22 F
6.8 F
+
+
+
+
+
1 F
C2
C3
C4
C5
C6
1H
1H
1H
1H
1H
L1
L2
L3
L4
L5
3.3k
R2
1k
1k
1k
1k
1k
R4
R4
R4
R4
R4
200Hz
800Hz
60Hz
3kHz
10kHz
1/4
OP470E
3.3k
R13
100
R14
REV. B
V
OUT