THS4521-HT_15 Datasheet, PDF (17/27 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT,RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

THS4521-HT
www.ti.com
Common-Mode and Power-Supply Rejection
The circuit shown in Figure 30 is used to measure the
CMRR. The signal from the network analyzer is
applied common-mode to the input. Figure 31 is used
to measure the PSRR of V_S+ and V_S–. The power
supply under test is applied to the network analyzer
dc offset input. For both CMRR and PSRR, the output
is probed using a Tektronix high-impedance
differential probe across the 953-Ω resistor and
referred to the amplifier output by adding back the
0.42-dB as a result of the voltage divider on the
output. For these tests, the resistors are matched for
best results.
V_IN+
From
Network
Analyzer
Calibrated
Differential 52.3 W
Probe
Open
1 kW
PD
0.22 mF
1 kW
1 kW
V_S+
THS452x
V_OCM
V_S-
1 kW
24.9 W
24.9 W
Measure with
953 W Differential
Probe
Open
0.22 mF
Figure 30. CMRR Test Circuit
Open
Open
Open
Power
Supply
Network
Analyzer
1 kW
52.3 W
PD
0.22 mF
1 kW
52.3 W
1 kW
V_S+
Calibrated Differential
Probe
Across
V_S+ and GND
THS452x
V_OCM
V_S-
1 kW
24.9 W
24.9 W
Measure with
Differential
953 W
Probe
Across R_OT
Open
0.22 mF
SBOS548D – APRIL 2011 – REVISED MAY 2012
V_OCM Input
The circuit illustrated in Figure 32 is used to measure
the frequency response and input impedance 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 33 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
Open
Open
1 kW
49.9 W
PD
0.22 mF
1 kW
49.9 W
1 kW
V_S+
THS452x
V_OCM
V_S
1 kW
499 W
499 W
Measurement
Point for Bandwidth
R_CM
Calibrated
Measurement ^Differential
Point for Z_IN
Probe
Across
49.9 W
Resistor
49.9 W
From
Network
Analyzer
Figure 32. V_OCM Input Test Circuit
Open
Open
Open
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
space
Figure 31. PSRR Test Circuit
Figure 33. V_OCM Transient Response and Slew
Rate Test Circuit
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