AD600/AD602
C1LO
INPUT
1V rms
MAX
(SINE WAVE)
A1HI
A1LO
GAT1
GAT2
A2LO
A2HI
C2LO
1
2
3
4
REF
5
–
6
7
8
A2
10
+
–
A1
16
15
14
13
12
11
C1HI
A1CM
A1OP
VPOS
VNEG
A2OP
A2CM
C2HI
+5V
DEC
–5V
DEC
C1
0.1µF
R1
133kΩ
C2
0.1µF
R4
133kΩ
R2
487Ω
R3
200Ω
C1LO
A1HI
A1LO
GAT1
GAT2
A2LO
U3B
1/4
AD713
A2HI
C2LO
1
2
3
4
REF
5
–
6
7
8
A2
10
+
–
A1
16
15
14
13
12
C1HI
A1CM
A1OP
VPOS
VNEG
U3A
1/4
AD713
R5
1.58kΩ
C3
220pF
C4
2µF
V
OUT
+5V
DEC
–5V
DEC
11 A2OP
A2CM
C2HI
U1 AD600
9
+5V
FB
+5V
DEC
–5V
DEC
FB
–5V
POWER SUPPLY
DECOUPLING
NETWORK
+5V DEC
R15
19.6kΩ
R16
6.65kΩ
0.1µF
–5V
–2dB
–62.5mV
R6
10kΩ
R7
127Ω
0dB
R8
127Ω
+2dB
+62.5mV
R9
10kΩ
+5V
0.1µF
C5
22µF
+5V DEC
1 VINP
NC
–5V
DEC
2
VPOS 14
13 NC
12 NC
11 NC
COMM 10
LDLO
V
RMS
9
U3C
8
+316.2mV
1/4
AD713
00538-045
U4
AD636
3 VNEG
4 CAVG
NC
NC
5 VLOG
6 BFOP
7 BFIN
R14
301kΩ
Q1
2N3906
R13
3.01kΩ
R12
11.3kΩ
Figure 47. RMS Responding AGC Circuit with 100 dB Dynamic Range
A 100 dB RMS/AGC SYSTEM WITH MINIMAL GAIN
ERROR (PARALLEL GAIN WITH OFFSET)
used equally well as an accurate measurement system. It accepts
inputs of 10 μV to 1 V rms (−100 dBV to 0 dBV) with generous
overrange. Figure 48 shows the logarithmic output, V
LOG
, which
is accurately scaled 1 V per decade, that is, 50 mV/dB, with an
intercept (V
LOG
= 0) at 3.16 mV rms (−50 dBV). Gain offsets of
±2 dB were introduced between the amplifiers, provided by the
±62.5 mV introduced by R6 to R9. These offsets cancel a small
gain ripple that arises in the X-AMP from its finite interpolation
error, which has a period of 18 dB in the individual VCA
sections. The gain ripple of all three amplifier sections without
this offset (in which case, the gain errors simply add) is shown
in Figure 49; it is still a remarkably low ±0.25 dB over the
108 dB range from 6 μV to 1.5 V rms. However, with the gain
offsets connected, the gain linearity remains under ±0.1 dB over
the specified 100 dB range (see Figure 50).
LOGARITHMIC OUTPUT (V)
5
4
3
2
1
0
–1
–2
–3
–4
–5
1µ
10µ
100µ
1m
10m
100m
1
10
00538-046
Figure 48. V
LOG
Plotted vs. V
IN
for Figure 47’s Circuit Showing 120 dB AGC Range
Rev. E | Page 22 of 28
+
+
U2 AD600
9
R11
46.4kΩ
R10
3.16kΩ
C6
4.7µF
V
LOG
NC = NO CONNECT
INPUT SIGNAL (V rms)
AD [ ANALOG DEVICES ]
