REV. D

OP97

–7–

APPLICATIONS INFORMATION

The OP97 is a low power alternative to the industry standard

precision op amp, the OP07. The OP97 may be substituted

directly into OP07, OP77, 725, 112/312, and 1012 sockets with

improved performance and/or less power dissipation, and may

be inserted into sockets conforming to the 741 pinout if nulling

circuitry is not used. Generally, nulling circuitry used with earlier

generation amplifiers is rendered superfluous by the OP97’s

extremely low offset voltage, and may be removed without com-

promising circuit performance.

Extremely low bias current over the full military temperature

range makes the OP97 attractive for use in sample-and-hold

amplifiers, peak detectors, and log amplifiers that must operate

over a wide temperature range. Balancing input resistances is

degraded only minimally by high source resistance, even when

unbalanced.

The input pins of the OP97 are protected against large differen-

tial voltage by back-to-back diodes. Current-limiting resistors

are not used so that low noise performance is maintained. If

differential voltages above

± 1 V are expected at the inputs,

series resistors must be used to limit the current flow to a

maximum of 10 mA. Common-mode voltages at the inputs are

not restricted, and may vary over the full range of the supply

voltages used.

The OP97 requires very little operating headroom about the

supply rails, and is specified for operation with supplies as low

OP97

TO 100k

–V

+V

Figure 1. Optional Input Offset Voltage Nulling

and Overcompensation Circuits

Figure 2. Small-Signal Transient Response

as

±2 V. Typically, the common-mode range extends to within

one volt of either rail. The output typically swings to within one

volt of the rails when using a 10 k

Ω load.

Offset nulling is achieved utilizing the same circuitry as an

OP07. A potentiometer between 5 k

Ω and 100 kΩ is connected

between pins 1 and 8 with the wiper connected to the positive

supply. The trim range is between 300

µV and 850 µV, depend-

ing upon the internal trimming of the device.

AC PERFORMANCE

The OP97’s ac characteristics are highly stable over its full

operating temperature range. Unity-gain small-signal response

is shown in Figure 2. Extremely tolerant of capacitive loading

on the output, the OP97 displays excellent response even with

1000 pF loads (Figure 3). In large-signal applications, the

input protection diodes effectively short the input to the output

during the transients if the amplifier is connected in the usual

unity-gain configuration. The output enters short-circuit current

limit, with the flow going through the protection diodes. Improved

large-signal transient response is obtained by using a feedback

resistor between the output and the inverting input. Figure 4

shows the large-signal response of the OP97 in unity gain with a

10 k

Ω feedback resistor. The unity gain follower circuit is shown

in Figure 5.

The overcompensation pin may be used to increase the phase

margin of the OP97, or to decrease gain-bandwidth product at

gains greater than 10.

Figure 3. Small-Signal Transient Response