OP297 Datasheet, PDF (11/16 Pages) Analog Devices – Dual Low Bias Current Precision Operational Amplifier

8/21/97 4:00 PM
R₂
33kΩ
C₂
100pF
6_–
1/2
7
OP-297
I_O 5 ₊
OP297
V_OUT
R₁
V_IN
33kΩ
I_IN
C₁
100pF
V+
2_{– 8}
1/2
1
3
OP-297
+₄
Q_{1 1}
2
3
7
6 _Q2
5
R₅
2kΩ
MAT-04E
I_REF
14
13 _Q4
8
12
Q₃ ⁹
10
R₃
50kΩ
R₄
50kΩ
V–
Figure 35. Square-Root Amplifier
–15V
In these circuits, I_REF is a function of the negative power supply.
To maintain accuracy, the negative supply should be well regu-
lated. For applications where very high accuracy is required, a
voltage reference may be used to set I_REF. An important consid-
eration for the squaring circuit is that a sufficiently large input
voltage can force the output beyond the operating range of the
output op amp. Resistor R4 can be changed to scale I_REF, or R1,
and R2 can be varied to keep the output voltage within the
usable range.
Unadjusted accuracy of the square-root circuit is better than
0.1% over an input voltage range of 100 mV to 10 V. For a
similar input voltage range, the accuracy of the squaring circuit
is better than 0.5%.
OP297 SPICE MACRO-MODEL
Figures 36 and 37 show the node end net list for a SPICE
macro model of the OP297. The model is a simplified version of
the actual device and simulates important dc parameters such as
V_OS, I_OS, I_B, A_VO, CMR, V_O and I_SY. AC parameters such as
slew rate, gain and phase response and CMR change with fre-
quency are also simulated by the model.
The model uses typical parameters for the OP297. The poles
and zeros in the model were determined from the actual open
and closed-loop gain and phase response of the OP297. In this
way, the model presents an accurate ac representation of the
actual device. The model assumes an ambient temperature
of 25°C.
REV. D
–11–