AD603
VC1
VC2
VIN
1
GPOS
GNEG
VINP
COMM
VPOS
8
VOUT
7
VNEG
6
FDBK
5
VPOS
VOUT
VNEG
2.15kΩ
5.6pF
00539-031
AD603
2
3
Optionally, when a resistor is placed from FDBK to COMM,
higher gains can be achieved. This fourth mode is of limited
value because of the low bandwidth and the elevated output
offsets; it is thus not included in Figure 30, Figure 31, or
The gain of this amplifier in the first two modes is set by the
ratio of on-chip laser-trimmed resistors. While the ratio of these
resistors is very accurate, the absolute value of these resistors
can vary by as much as ±20%. Therefore, when an external
resistor is connected in parallel with the nominal 6.44 kΩ ± 20%
internal resistor, the overall gain accuracy is somewhat poorer.
The worst-case error occurs at about 2 kΩ (see Figure 34).
1.2
–1:VdB (OUT) – (–1):VdB (O
REF
)
1.0
0.8
00539-032
4
Figure 31. 0 dB to 40 dB; 30 MHz Bandwidth
VC1
VC2
VIN
1
GPOS
GNEG
VINP
COMM
VPOS
8
VOUT
7
VNEG
6
VPOS
VOUT
VNEG
AD603
2
3
4
FDBK
5
18pF
0.6
GAIN ERROR (dB)
0.4
0.2
0
–0.2
–0.4
–0.6
Figure 32. 10 dB to 50 dB; 9 MHz to Set Gain
52
50
48
46
44
GAIN (dB)
–1:VdB (OUT)
–2:VdB (OUT)
40
38
36
34
32
100
1k
R
EXT
(Ω)
10k
100k
1M
00539-033
100
1k
R
EXT
(Ω)
10k
100k
1M
Figure 34. Worst-Case Gain Error, Assuming Internal Resistors Have a
Maximum Tolerance of −20% (Top Curve) or = 20% (Bottom Curve)
30
10
Figure 33. Gain vs. R
EXT
, Showing Worst-Case Limits Assuming Internal
Resistors Have a Maximum Tolerance of 20%
While the gain bandwidth product of the fixed-gain amplifier is
about 4 GHz, the actual bandwidth is not exactly related to the
maximum gain. This is because there is a slight enhancing of
the ac response magnitude on the maximum bandwidth range,
due to higher order poles in the open-loop gain function; this
mild peaking is not present on the higher gain ranges. Figure 30,
be added to extend the frequency response in high gain modes.
Rev. H | Page 13 of 24
00539-034
42
VdB (OUT)
–0.8
–1.0
10
VdB (OUT) – VdB (O
REF
)
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