OP275

REV. A

–9–

+15V

+

0.1µF

2

3

8

1

4

2k

Ω

–15V

10µF

0.1µF

1/2

OP275

10µF

+

Figure 12. Unity Gain Follower

0.1µF

+15V

+

10µF

2

3

8

1

4

2k

Ω

–15V

10µF

0.1µF

10pF

4.99k

Ω

2.49k

Ω

4.99k

Ω

+

1/2

OP275

Figure 13. Unity Gain Inverter

In inverting and noninverting applications, the feedback resis-

tance forms a pole with the source resistance and capacitance

create excess phase shift and even oscillation. A small capacitor,

pletely removed.

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 k

Ω 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

Ω. Keeping the values of these resis-

tors small has the added benefits of reducing the thermal noise

0P275

FOR MINIMUM DISTORTION

Figure 15. Balanced Input Impedance to Minimize

Distortion in Noninverting Amplifier Circuits

16–20V

0.1µF

V+

±5V

1k

Ω

D1

D2

+15V

2N4416

1k

Ω

D3

D4

OUTPUT

(TO SCOPE)

1µF

10k

Ω

IC2

2k

Ω

750

Ω

2N2222A

15k

Ω

–15V

1N4148

DUT

1/2 OP260AJ

16–20V

0.1µF

10k

Ω

–+

+

–

SCHOTTKY DIODES D1–D4 ARE

HEWLETT-PACKARD HP5082-2835

IC1 IS 1/2 OP260AJ

IC2 IS PMI OP41EJ

V–

222

Ω

Figure 11. OP275’s Settling Time Test Fixture