AD883B3 データシートの表示（PDF） - Analog Devices
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AD883B3 Datasheet PDF : 20 Pages
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AD600/AD602
C1LO
1
A1HI 2
A1LO
3
GAT1
4
GAT2
5
A2LO
6
A2HI
7
C2LO
8
A1
REF
A2
U1 AD600
C1HI
16
A1CM
15
A1OP
14
VPOS
13
VNEG
12
A2OP
11
10 A2CM
C2HI
9
C1
0.1µF
U3A
R2
100Ω
+6V DEC
–6V DEC
R1
133kΩ
1/4
AD713
C2
0.1µF
R5
5.36kΩ
R4
C3
133kΩ 0.001µF
U3B
1/4
AD713
C1LO
1
C1HI
16
A1HI 2
A1CM
15
C4
A1LO
A1
A1OP
2µF
3
14
GAT1
4
GAT2
5
VPOS
13
REF
VNEG
12
+6V DEC
–6V DEC
A2LO
6
A2HI
7
11 A2OP
A2
10 A2CM
C2LO
C2HI
8
9
U2 AD600
VOUT
R3 R17
200Ω 115Ω
INPUT
+6V
R6
3.4kΩ
R7 R8
1kΩ 294Ω
R9 R16
1kΩ 287Ω
C5
22µF
+6V DEC
+6V DEC
R15
5.11kΩ
R14
R13
7.32kΩ 866Ω
1 VINP
VPOS 14
U4
NC 2 AD636
13 NC
–6V DEC
3 VNEG
12 NC
4 CAVG
NC 5 VLOG
11 NC R10
3.16kΩ
COMM 10
R11
56.2kΩ
C6
4.7µF
NC 6 BFOP LDLO 9
7 BFIN
VRMS 8
U3C
+316.2mV
1/4
AD713
R12
1kΩ
NC = NO CONNECT
+6V
FB
+6V DEC
0.1µF
–6V DEC
FB
0.1µF
–6V
POWER SUPPLY
DECOUPLING NETWORK
VLOG
Figure 29. 120 dB Dynamic Range RMS Responding Circuit Optimized for S/N Ratio
resistance of U1A as well as the fixed 6 dB attenuation provided
5
by R2 and the input resistance of U1B are included both to set
4
VLOG to read 0 dB when VIN is 3.16 mV rms and to center the
100 dB range between 10 µV rms and 1 V rms input. R5 and
3
C3 provide a 3 dB noise bandwidth of 30 kHz. R12 to R15
2
change the scaling from 625 mV/decade at the control inputs to
1
1 V/decade at the output and at the same time center the dy-
0
namic range at 60 dB, which occurs if the VG of U1B is equal to
zero. These arrangements ensure that the VLOG will still fit
–1
within the ± 6 V supplies.
–2
Figure 30 shows VLOG to be linear over a full 120 dB range.
Figure 31 shows the error ripple due to the individual gain func-
tions which is bounded by ± 0.2 dB (dotted lines) from 6 µV to
2 V. The small perturbations at about 200 µV 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 VAGC which remains very close to its set value
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 kΩ), and only the gain
control was varied, using an external source. The rms value of
the noise was then measured at VOUT and expressed as an S/N
–3
–4
–5
1µV 10µV 100µV 1mV 10mV 100mV 1V
10V
INPUT SIGNAL – V RMS
Figure 30. VLOG Is Essentially Linear Over the Full 120 dB
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.
–16–
REV. A
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