The AD515A is a monolithic FET-input operational amplifier
with a guaranteed maximum input bias current of 75 fA
(AD515AL). The AD515A is a monolithic successor to the
industry standard AD515 electrometer, and will replace the
AD515 in most applications. The AD515A also delivers laser-trimmed
offset voltage, low drift, low noise and low power, a
combination of features not previously available in ultralow bias
current circuits. All devices are internally compensated, protected
against latch-up and are short circuit protected.
The AD515A's combination of low input bias current, low
offset voltage and low drift optimizes it for a wide variety of
electrometer and very high impedance buffer applications
including photocurrent detection, vacuum ion-gage measurement,
long-term precision integration and low drift sample/hold
applications. This amplifier is also an excellent choice for all forms
of biomedical instrumentation such as pH/pIon sensitive electrodes,
very low current oxygen sensors, and high impedance
biological microprobes. In addition, the low cost and pin
compatibility of the AD515A with standard FET op amps will
allow designers to upgrade the performance of present systems
at little or no additional cost. The 10 15 W common-mode input
impedance ensures that the input bias current is essentially
independent of common-mode voltage.
As with previous electrometer amplifier designs from Analog
Devices, the case is brought out to its own connection (Pin 8)
so it can be independently connected to a point at the same
potential as the input, thus minimizing stray leakage to the case.
This feature will also shield the input circuitry from external
noise and supply transients.
The AD515A is available in three versions of bias current and
offset voltage, the "J", "K" and "L"; all are specified for rated
performance from 0°C to +70°C and supplied in a hermetically
sealed TO-99 package.
