NJM2723 View Datasheet(PDF) - Japan Radio Corporation
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NJM2723 Datasheet PDF : 11 Pages
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NJM2723
■ Application Note
● Choice of feedback resistor and gain resistor for current feedback operational Amplifier
The NJM2723 is a current feedback operational amplifier. Closed-loop bandwidth depends on the feedback resistor
value. Table1 shows recommended resistor values for a variety of useful closed-loop gains and supply voltages.
Figure1. Formula of non−inverting / inverting amplifier
RF
RG
-
VO
+
VIN
RF
RG
VIN
-
VO
+
Gv=1+RF/RG
Gv= -RF/RG
Table1. -3dB Bandwidth vs. Closed−loop Gain and Resistance Value
V+/V-=±15V
Closed-Loop Gain
+1
+2
+10
-1
-10
RF[Ω]
750
680
680
680
680
RG[Ω]
-
680
75
680
68
-3dB BW[MHz]
120
76
20
65
25
V+/V-=±5V
Closed-Loop Gain
+1
+2
+10
-1
-10
RF[Ω]
680
680
620
680
680
RG[Ω]
-
680
68
680
68
-3dB BW[MHz]
85
52
15
50
20
● In case of using Voltage follower
The feedback resistance must be inserted when using a current feedback amplifier as the voltage follower.
A current feedback amplifier cannot be used by connecting output pin and inverting input pin directly. (Figure2)
Figure2. Voltage follower circuit
RF
-
VO
VIN
+
● In case of using capacitive Feedback
For a current feedback amplifier stability operation, do not use a compensation capacitor in parallel with feedback
resistance. The dynamic impedance of capacitor in the feedback loop reduces the amplifier's stability.
Figure3. Non-stability circuit example
C
RF
RG
-
VO
+
VIN
(a). C connects in paraliel with RF
RF
RG
-
VO
C
+
VIN
(b). C connects to input pin
- 10 -
Ver.2009-10-28
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