AD602 AD [Analog Devices], AD602 Datasheet - Page 16

• Manufacturer Part Number: AD602
• Description: Dual, Low Noise, Wideband Variable Gain Amplifiers
• Manufacturer: AD [Analog Devices]

AD600/AD602
resistance of U1A as well as the fixed 6 dB attenuation provided
by R2 and the input resistance of U1B are included both to set
V
100 dB range between 10 V rms and 1 V rms input. R5 and
zero. These arrangements ensure that the V
within the 6 V supplies.
Figure 30 shows V
Figure 31 shows the error ripple due to the individual gain func-
tions which is bounded by 0.2 dB (dotted lines) from 6 V to
of 316 mV rms over the full 120 dB range.
To more directly compare the signal-to-noise ratios in the
“simultaneous” and “sequential” modes of operation, all inter-
stage attenuation was eliminated (R2 and R3 in Figure 25, R2 in
Figure 29), the input of U1A was shorted, R5 was selected to
provide a 20 kHz bandwidth (R5 = 7.87 k ), and only the gain
control was varied, using an external source. The rms value of
the noise was then measured at V
C3 provide a 3 dB noise bandwidth of 30 kHz. R12 to R15
change the scaling from 625 mV/decade at the control inputs to
1 V/decade at the output and at the same time center the dy-
namic range at 60 dB, which occurs if the V
2 V. The small perturbations at about 200 V and 20 mV,
caused by the impracticality of matching the gain functions per-
fectly, are the only sign that the gains are now sequential. Fig-
ure 32 is a plot of V
LOG
to read 0 dB when V
200
R3
115
R17
C1LO
A1LO
GAT1
A2LO
GAT2
C2LO
A1HI
A2HI
INPUT
1
2
3
4
5
6
7
8
LOG
AGC
U1 AD600
Figure 29. 120 dB Dynamic Range RMS Responding Circuit Optimized for S/N Ratio
to be linear over a full 120 dB range.
which remains very close to its set value
A1
A2
IN
REF
+6V DEC
is 3.16 mV rms and to center the
R15
5.11k
R14
7.32k
16
15
14
13
12
11
10
9
OUT
C1HI
A1CM
A1OP
VPOS
VNEG
A2OP
A2CM
C2HI
866
and expressed as an S/N
R13
+6V DEC
–6V DEC
R12
1k
LOG
G
–6V DEC
of U1B is equal to
133k
will still fit
0.1 F
C1
R1
NC
NC
NC
1
5
6
7
2
3
4
133k
0.1 F
C2
U3A
VINP
VNEG
CAVG
VLOG
BFOP
BFIN
R4
1/4
AD713
AD636
+6V
U4
22 F
0.001 F
C5
5.36k
R5
COMM
VPOS
LDLO
3.4k
V
C3
R6
RMS
–16–
100
R2
14
13
12
11
10
9
8
Figure 30. V
Range
ratio relative to 0 dBV, this being almost the maximum output
capability of the AD600. Results for the simultaneous mode can
be seen in Figure 33. The S/ N ratio degreades uniformly as the
gain is increased. Note that since the inverting gain control was
used, the gain in this curve and in Figure 34 decreases for more
positive values of the gain-control voltage.
1k
R7
NC
NC
NC
U3B
3.16k
+316.2mV
294
1/4
AD713
R10
R8
–1
–2
–3
–4
–5
5
4
3
2
1
0
+6V DEC
R11
56.2k
1 V
1k
R9
NC = NO CONNECT
4.7 F
LOG
U3C
C6
1/4
AD713
287
R16
10 V
C1LO
A1LO
GAT1
GAT2
A2LO
C2LO
Is Essentially Linear Over the Full 120 dB
A1HI
A2HI
1
2
3
4
5
6
7
8
100 V
INPUT SIGNAL – V RMS
U2 AD600
+6V DEC
–6V DEC
V
LOG
1mV
DECOUPLING NETWORK
A2
A1
REF
POWER SUPPLY
FB
FB
16
15
14
13
12
11
10
+6V
–6V
10mV
9
C1HI
A1CM
A1OP
VPOS
VNEG
A2OP
A2CM
C2HI
0.1 F
0.1 F
100mV
+6V DEC
–6V DEC
1V
2 F
C4
10V
REV. A
V
OUT