AD603 Analog Devices, Inc., AD603 Datasheet - Page 13

• Manufacturer Part Number: AD603
• Description: Low Noise, 90 Mhz Variable-gain Amplifier
• Manufacturer: Analog Devices, Inc.

Figure 33. Gain vs. R
VIN
VIN
52
50
48
46
44
42
40
38
36
34
32
30
10
Resistors Have a Maximum Tolerance of 20%
Figure 31. 0 dB to 40 dB; 30 MHz Bandwidth
Figure 32. 10 dB to 50 dB; 9 MHz to Set Gain
VC1
VC2
VC1
VC2
100
VdB (OUT)
EXT
, Showing Worst-Case Limits Assuming Internal
1
2
3
4
1
2
3
4
GPOS
GNEG
VINP
COMM
GPOS
GNEG
VINP
COMM
–1:VdB (OUT)
1k
AD603
AD603
R
EXT
VNEG
VPOS
VOUT
FDBK
VPOS
VOUT
VNEG
FDBK
(Ω)
10k
–2:VdB (OUT)
8
7
6
5
8
7
6
5
VPOS
VNEG
VPOS
VNEG
18pF
100k
2.15kΩ
5.6pF
VOUT
VOUT
1M
Rev. H | Page 13 of 24
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
Figure 32.
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).
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,
Figure 31, and Figure 32 show how an optional capacitor may
be added to extend the frequency response in high gain modes.
Figure 34. Worst-Case Gain Error, Assuming Internal Resistors Have a
Maximum Tolerance of −20% (Top Curve) or = 20% (Bottom Curve)
–0.2
–0.4
–0.6
–0.8
–1.0
1.2
1.0
0.8
0.6
0.4
0.2
0
10
100
1k
R
EXT
–1:VdB (OUT) – (–1):VdB (O
(Ω)
10k
VdB (OUT) – VdB (O
100k
REF
REF
AD603
)
)
1M