RHF484 STMICROELECTRONICS [STMicroelectronics], RHF484 Datasheet - Page 13

• Manufacturer Part Number: RHF484
• Description: Rad-hard precision quad operational amplifier
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

RHF484
3
Figure 24. Low gain configuration
Achieving good stability at low gain
At low frequencies, the RHF484 can be used in a low gain configuration as shown in
Figure
can be set close to 1 V/V (0 dB), and is reduced to its simplest expression G1=1+Rfb/Rg.
Therefore, an R-C cell is added in the gain network so that the gain is increased (up to 5) at
higher frequencies (where the stability of the amplifier could be affected). At higher
frequencies, the gain becomes G2=1+Rfb/(Rg//R).
Rg becomes a complex impedance. The closed-loop gain features a variation in frequency
and can be expressed as:
where a pole appears at 1/2πRC and a zero at G1/2π(G1R+Rfb)C. The frequency can be
plotted as shown in
Table 6.
24. At lower frequencies, the stability is not affected by the value of the gain, which
G1 (V/V)
1.1
2
3
4
5
External components versus low-frequency gain
Figure
Not connected
25.
R (Ω)
Gain
510
510
510
510
Doc ID 17351 Rev 1
=
G1
Figure 25. Closed-loop gain
1
------------------------------------------------------------ -
Not connected
+
jCω
C (nF)
1
×
1
1
1
1
+
⎛
⎝
jCRω
G1R
---------------------------- -
Achieving good stability at low gain
G1
+
Rfb
⎞
⎠
Rg (Ω)
750
820
20k
2k
1k
Rfb (Ω)
2.4k
3.3k
2k
2k
2k
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