THS4521 Datasheet, PDF (25/65 Pages) Texas Instruments – VERY LOW POWER, NEGATIVE RAIL INPUT, RAIL-TO-RAIL OUTPUT, FULLY DIFFERENTIAL AMPLIFIER

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8.2 Functional Block Diagram
(RGT Package) FB+
IN–
IN+
(RGT Package) FB–
THS4521, THS4522, THS4524
SBOS458H – DECEMBER 2008 – REVISED JUNE 2015
Vs+
–
High-Aol +
Differential I/O
Amplifier –
+
5 kΩ
5 kΩ
OUT+
OUT–
Vs+
275 kΩ
PD
CMOS
Buffer
–
Vcm
Error
Amplifier
+
Vocm
275 kΩ
Vs–
8.3 Feature Description
8.3.1 Frequency Response
The circuit shown in Figure 54 is used to measure the frequency response of the circuit.
A network analyzer is used as the signal source and the measurement device. The output impedance of the
network analyzer is dc-coupled and is 50 Ω. R_IT and R_G are chosen to impedance-match to 50 Ω and maintain
the proper gain. To balance the amplifier, a 49.9-Ω resistor to ground is inserted across R_IT on the alternate
input.
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 because of the voltage divider on the output.
V_IN+
From
50-W
Source
Calibrated
Differential
Probe
Across
R_IT
Open
Installed to
Balance
Amplifier
49.9 W
R_G
R_IT
PD
0.22 mF
R_G
R_IT
1 kW
V_S+
THS452x
V_OCM
V_S-
1 kW
24.9 W
24.9 W
953 W
Measure with
Differential
Probe
Across R_OT
Open
0.22 mF
Figure 54. Frequency Response Test Circuit
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