OP470GPZ Datasheet, PDF (14/16 Pages) Analog Devices – Very Low Noise Quad Operational Amplifier

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.
R5
100k⍀
D2
1N4148
2N5434
R2
10k⍀
R1
2k⍀
V_IN
1/4
OP470E
A
V_OUT – –5V_IN
R4
10k⍀
R3
2k⍀
D1
1/4
1N4148
OP470E
B
C1 R6
1/4
1␮F 1M⍀ OP470E
C
R4
10M⍀
␶ = 1 SECOND
R7
C2
10k⍀ _10␮F
+
V+
R6
10k⍀
Figure 17. Squelch Amplifier
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.
C1
0.47␮F
V_IN
R1
47k⍀
1/4
OP470E
R2
3.3k⍀
1/4
OP470E
R3
680⍀
C2
6.8␮F
+
L1
1H
TANTALUM
R5
680⍀
C3
1␮F
+
L2
1H
TANTALUM
R7
680⍀
C4
0.22␮F
+
L3
1H
TANTALUM
R9
680⍀
C5
0.047␮F
+
L4
1H
TANTALUM
R11
680⍀
C6
0.022␮F
+
L5
1H
TANTALUM
R4
1k⍀
60Hz
R4
1k⍀
200Hz
R4
1k⍀
800Hz
R4
1k⍀
3kHz
R4
1k⍀
10kHz
R13
3.3k⍀
R14
100⍀
V_OUT
Figure 18. Five-Band Low Noise Graphic Equalizer
–14–
REV. B