LT1113_15 Datasheet, PDF (11/16 Pages) Linear Technology – Dual Low Noise, Precision, JFET Input Op Amp

APPLICATI S I FOR ATIO
INPUT: ±5.2V Sine Wave
LT1113 Output
LT1113
OPA2111 Output
Figure 3. Voltage Follower with Input Exceeding the Common Mode Range ( V_S = ±5V)
resistor (R_B) will reduce the IR errors due to I_B by an order
of magnitude. A further reduction of IR errors can be
achieved by using a DC servo circuit shown in the applica-
tions section of this data sheet. The DC servo has the
advantage of reducing a wide range of IR errors to the
millivolt level over a wide temperature variation. The
preservation of dynamic range is especially important
when reduced supplies are used, since input bias currents
can exceed the nanoamp level for die temperatures
over 85°C.
To take full advantage of a wide input common mode
range, the LT1113 was designed to eliminate phase rever-
sal. Referring to the photographs shown in Figure 3, the
LT1113 is shown operating in the follower mode (A_V = +1)
at ±5V supplies with the input swinging ±5.2V. The output
of the LT1113 clips cleanly and recovers with no phase
reversal, unlike the competition as shown by the last
photograph. This has the benefit of preventing lock-up in
servo systems and minimizing distortion components.
The effect of input and output overdrive on one amplifier
has no effect on the other, as each amplifier is biased
independently.
Advantages of Matched Dual Op Amps
In many applications the performance of a system
depends on the matching between two operational ampli-
fiers rather than the individual characteristics of the two op
amps. Two or three op amp instrumentation amplifiers,
tracking voltage references and low drift active filters
are some of the circuits requiring matching between two
op amps.
The well-known triple op amp configuration in Figure 4
illustrates these concepts. Output offset is a function of the
difference between the two halves of the LT1113. This
error cancellation principle holds for a considerable
number of input referred parameters in addition to
offset voltage and bias current. Input bias current will
be the average of the two noninverting input currents
(I_B+). The difference between these two currents (∆I_B+)
is the offset current of the instrumentation amplifier.
Common mode and power supply rejections will be
dependent only on the match between the two amplifiers
(assuming perfect resistor matching).
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