OP275_ データシートの表示（PDF） - Analog Devices
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OP275_ Datasheet PDF : 12 Pages
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16–20V
–+
0.1µF
V+
DUT
V–
0.1µF
+–
16–20V
±5V
RL
1kΩ
D1
1N4148
+15V
1kΩ
2N4416 1/2 OP260AJ
D2
RF
2kΩ
D3
10kΩ
OUTPUT
D4 (TO SCOPE)
1µF
RG
222Ω
2N2222A
15kΩ
–15V
10kΩ
IC2
750Ω
SCHOTTKY DIODES D1–D4 ARE
HEWLETT-PACKARD HP5082-2835
IC1 IS 1/2 OP260AJ
IC2 IS PMI OP41EJ
Figure 11.␣ OP275’s Settling Time Test Fixture
+15V
0.1µF
10µF
+
CFB
RFB
OP275
2
8
1/2
1
VIN
3 OP275
4 0.1µF
10µF
+
RL
2kΩ
VOUT
–15V
Figure 12. Unity Gain Follower
+15V
0.1µF
10µF
+
10pF
VIN
4.99kΩ
2.49kΩ
2
8
1/2
1
3 OP275
4
10µF
0.1µF
+
4.99kΩ
2kΩ
VOUT
–15V
Figure 13. Unity Gain Inverter
In inverting and noninverting applications, the feedback resis-
tance forms a pole with the source resistance and capacitance
(RS and CS) and the OP275’s input capacitance (CIN), as shown
in Figure 14. With RS and RF in the kilohm range, this pole can
create excess phase shift and even oscillation. A small capacitor,
CFB, in parallel and RFB eliminates this problem. By setting RS
(CS + CIN) = RFBCFB, the effect of the feedback pole is com-
pletely removed.
RS
CS
CIN
VOUT
Figure 14. Compensating the Feedback Pole
Attention to Source Impedances Minimizes Distortion
Since the OP275 is a very low distortion amplifier, careful atten-
tion should be given to source impedances seen by both inputs.
As with many FET-type amplifiers, the p-channel JFETs in the
OP275’s input stage exhibit a gate-to-source capacitance that
varies with the applied input voltage. In an inverting configura-
tion, the inverting input is held at a virtual ground and, as such,
does not vary with input voltage. Thus, since the gate-to-source
voltage is constant, there is no distortion due to input capaci-
tance modulation. In noninverting applications, however, the
gate-to-source voltage is not constant. The resulting capacitance
modulation can cause distortion above 1 kHz if the input im-
pedance is > 2 kΩ and unbalanced.
Figure 15 shows some guidelines for maximizing the distortion
performance of the OP275 in noninverting applications. The
best way to prevent unwanted distortion is to ensure that the
parallel combination of the feedback and gain setting resistors
(RF and RG) is less than 2 kΩ. Keeping the values of these resis-
tors small has the added benefits of reducing the thermal noise
RG
RF
RS*
VIN
0P275
VOUT
* RS = RG//RF IF RG//RF > 2kΩ
FOR MINIMUM DISTORTION
Figure 15. Balanced Input Impedance to Minimize
Distortion in Noninverting Amplifier Circuits
REV. A
–9–
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