THS4521 Datasheet, PDF (28/65 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521, THS4522, THS4524
SBOS458H – DECEMBER 2008 – REVISED JUNE 2015
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Feature Description (continued)
8.3.5 V_OCM Input
The circuit illustrated in Figure 59 is used to measure the frequency response and skew rate of the V_OCM input.
Frequency response is measured using a Tektronix high-impedance differential probe, with
R_CM = 0 Ω at the common point of V_OUT+ and V_OUT–, formed at the summing junction of the two matched 499-Ω
resistors, with respect to ground. The input impedance is measured using a Tektronix high-impedance differential
probe at the V_OCM input with R_CM = 10 kΩ and the drop across the 10-kΩ resistor is used to calculate the
impedance seen looking into the amplifier V_OCM input.
The circuit shown in Figure 60 measures the transient response and slew rate of the V_OCM input. A 1-V step input
is applied to the V_OCM input and the output is measured using a 50-Ω oscilloscope input referenced back to the
amplifier output.
Open
1 kΩ
49.9 Ω
1 kΩ
V_S+
Open
Open
PD
0.22 μF
1 kW
49.9 Ω
THS452x
V_OCM
V_S
1 kW
499 Ω
499 Ω
Measurement
Point for Bandwidth
R_CM
Calibrated
Measurement ^Differential
Point for Z_IN
Probe
Across
49.9 Ω
Resistor
49.9 Ω
From
Network
Analyzer
Open
Open
Open
Figure 59. V_OCM Input Test Circuit
1 kW
52.3 W
1 kW
V_S+
PD
0.22 mF
1 kW
52.3 W
THS452x
V_OCM
V_S-
1 kW
499 W
499 W
49.9 W
To Oscilloscope
50-W Input
49.9 W
Step
Input
Figure 60. V_OCM Transient Response and Slew Rate Test Circuit
28
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