OP297_03 Datasheet, PDF (9/12 Pages) Analog Devices – Dual Low Bias Current Precision Operational Amplifier

OP297
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 consider-
ation 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 14 and 15 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 frequency
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.
99
2
–IN
1
+IN
R3
R4
C2
5
6
12
R_{IN2 8}
C_IN
I_OS
R_IN1 7
R1
3
D1
R2
E_OS
D2
9
Q1 Q2
10 11
R5 R6
4
I1
G1 R7
98
50
C6
C7
R11
R13
V2
13 _C4
D3
R8
15
16
C3
E1 R9
D4
14
V3
E_REF
G1 ^R10 C5
E2 R12 E3 R14 _G3 R15 C8
98
9
99
R16
I_SYS
D7
D8
D5 ₂₆
22
23
D6 ₂₇
G6
V4
V5 ²⁵
R17
50
28 29
G7
D9
G4
G5 ^D10
Figure 15. Macro Model
R18
L1
R19
REV. E
–9–