OP275 Ver la hoja de datos (PDF) - Analog Devices
Número de pieza
componentes Descripción
Fabricante
OP275 Datasheet PDF : 12 Pages
| |||
OP275
16V–20V
–+
0.1F
V+
DUT
V–
0.1F
+–
16V–20V
5V
RL
1k
D1
1N4148
+15V
1k
D3
2N4416 1/2 OP260AJ
OUTPUT
D4 (TO SCOPE)
D2
RF
2k
RG
222
2N2222A
10k
10k
750
1F
–
IC2
+
15k
–15V
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
0.1F
10F
+
CFB
RFB
2
–
8
1/2
1
VIN
3 OP275
+
4 0.1F
10F
+
RL
2k
VOUT
–
RS
CS
CIN
+
VOUT
Figure 14. Compensating the Feedback Pole
–15V
Figure 12. Unity Gain Follower
+15V
0.1F
10F
+
10pF
VIN
4.99k
2.49k
2– 8
1/2
1
3
OP275
+
4
10F
0.1F
+
4.99k
2k
VOUT
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 var-
ies with the applied input voltage. In an inverting configuration,
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 capacitance modu-
lation. 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 impedance is
greater than 2 k and unbalanced.
RG
RF
–
–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 completely removed.
RS*
OP275
VIN
+
VOUT
* RS = RG//RF IF RG//RF > 2k
FOR MINIMUM DISTORTION
Figure 15. Balanced Input Impedance to Minimize
Distortion in Noninverting Amplifier Circuits
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 k. Keeping the values of these resistors small
has the added benefits of reducing the thermal noise of the circuit
REV. C
–9–
Share Link: 