OPA625 Datasheet, PDF (23/44 Pages) Texas Instruments – OPAx625 High-Bandwidth, High-Precision, Low THD+N,16-Bit and 18-Bit Analog-to-Digital Converter (ADC) Drivers

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OPA625, OPA2625
SBOS688 – APRIL 2015
7 Parameter Measurement Information
7.1 DC Parameter Measurements
The circuit shown in Figure 63 is used to measure the dc input offset related parameters of the OPAx625. Input
offset voltage, power supply rejection ratio, common mode rejection ratio and open loop gain can be measured
with this circuit. The basic test procedure requires setting the inputs (the power-supply voltage, V_S, and the
common-mode voltage, V_CM), to the desired values. V_O is set to the desired value by adjusting the loop-drive
voltage while measuring V_O. After all inputs are configured, measure the input offset at the V_X measurement
point. Calculate the input offset voltage by dividing the measured result by 101. Changing the voltages on the
various inputs changes the input offset voltage. The input parameters can be measured according to the
relationships illustrated in Equation 1 through Equation 5.
RCOMP = 1 k  C_COMP = 0.1 2F
RB = 1.26 k 
V+
Loop ⁺
Drive _±
30 V
VOS
RA = 12.6 
OPA625
+
RIN = 12.6 
V-
VO
+
VCM
±
OPA551
VX
+
RLOAD
-30 V
Figure 63. DC-Parameters Measurement Circuit
V_OS

V_X
101
(1)
V_OSDrift

V_OS
Temperature
(2)
PSRR  ^VOS
V_SUPPLY
(3)
CMRR  ^VOS
V_CM
(4)
AOL  ^VO
V_OS
(5)
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