AD603
VC1
1
GPOS
VPOS
8
VPOS
AD603
VC2
2
GNEG
VOUT
7
VOUT
VIN
3
VINP
VNEG
6
VNEG
2.15kΩ
00539-031
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%. Thus, 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).
4
COMM
FDBK
5
5.6pF
Figure 31. 0 dB to 40 dB; 30 MHz Bandwidth
VC1
1
GPOS
VPOS
8
VPOS
AD603
VC2
2
GNEG
VOUT
7
VOUT
1.2
1.0
00539-032
VIN
3
VINP
VNEG
6
VNEG
–1:VdB (OUT) – (–1):VdB (O
REF
)
4
COMM
FDBK
5
0.8
0.6
0.4
DECIBELS
18pF
Figure 32. 10 dB to 50 db; 9 MHz to Set Gain
0.2
0
–0.2
–0.4
–0.6
–0.8
100
1k
R
EXT
(Ω)
10k
100k
1M
00539-034
52
50
48
46
44
DECIBELS
–1:VdB (OUT)
42
40
38
36
34
32
100
VdB (OUT)
–2:VdB (OUT)
–1.0
10
VdB (OUT) – VdB (O
REF
)
Figure 34. Worst-Case Gain Error, Assuming Internal Resistors have a
Maximum Tolerance of −20% (Top Curve) or =20% (Bottom Curve)
1k
R
EXT
(Ω)
10k
100k
1M
Figure 33. Gain vs. R
EXT,
Showing Worst-Case Limits Assuming Internal
Resistors have a Maximum Tolerance of 20%
00539-033
30
10
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. G | Page 13 of 20
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