RHF43B_11 STMICROELECTRONICS [STMicroelectronics], RHF43B_11 Datasheet - Page 11

• Manufacturer Part Number: RHF43B_11
• Description: Rad-hard precision bipolar single operational amplifier
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

RHF43B
3
Figure 23. Low gain configuration
C
R
Vin
Rg
Achieving good stability at low gains
At low frequencies, the RHF43B 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 5.
+
-
VDD
V
CC
Rfb = 2 kΩ
23. 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
C
L
= 100 pF
Figure
Not connected
24.
R (Ω)
Gain
510
510
510
510
Doc ID 13477 Rev 8
RL
1 kΩ
AM06122
Vout
=
G1
Figure 24. Closed-loop gain
0 dB
1
------------------------------------------------------------ -
Gain
(dB)
Not connected
+
jCω
C (nF)
Frequencies
where the
op-amp can
be used
1
×
1
1
1
1
+
⎛
⎝
jCRω
G1R
---------------------------- -
Achieving good stability at low gains
+20 dB/dec
G1
2 π(G1R+Rfb)C
+
Rfb
G1
2πRC
⎞
⎠
1
Rg (Ω)
750
820
20k
2k
1k
A
VD
Bandwidth
of the
op-amp at G2
- 20 dB/dec
G2=1+Rfb/(Rg//R)
Rfb (Ω)
G1=1+Rfb//Rg
Log frequency
Gain bandwidth
product
2.4k
3.3k
2k
2k
2k
AM06123
11/16