THS4521 Datasheet, PDF (26/65 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
www.ti.com
Feature Description (continued)
8.3.2 Distortion
The circuit shown in Figure 55 is used to measure harmonic and intermodulation distortion of the amplifier.
A signal generator is used as the signal source and the output is measured with a Rhode and Schwarz spectrum
analyzer. The output impedance of the HP signal generator is ac-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 0.22-μF capacitor and 49.9-
Ω resistor to ground are inserted across R_IT on the alternate input.
A low-pass filter is inserted in series with the input to reduce harmonics generated at the signal source. The level
of the fundamental is measured and then a notch filter is inserted at the output to reduce the fundamental so it
does not generate distortion in the input of the spectrum analyzer.
The transformer used in the output to convert the signal from differential to single-ended is an ADT1–1WT. It
limits the frequency response of the circuit so that measurements cannot be made below approximately 1 MHz.
V_IN+
From
50-W
Source
Open
Installed to
Balance
Amplifier
0.22 mF
49.9 W
R_G
R_IT
R_F
V_S+
PD
0.22 mF
R_G
R_IT
THS452x
V_OCM
V_S-
R_F
R_O
1:1
R_O
R_OT
Open
0.22 mF
V_{OUT To 50-W}
Test
Equipment
Figure 55. Distortion Test Circuit
8.3.3 Slew Rate, Transient Response, Settling Time, Output Impedance, Overdrive, Output Voltage, and
Turn-On/Turn-Off Time
The circuit shown in Figure 56 is used to measure slew rate, transient response, settling time, output impedance,
overdrive recovery, output voltage swing, and ampliifer turn-on/turn-off time. Turn-on and turn-off time are
measured with the same circuit modified for 50-Ω input impedance on the PD input by replacing the 0.22-μF
capacitor with a 49.9-Ω resistor. For output impedance, the signal is injected at V_OUT with V_IN open; the drop
across the 2x 49.9-Ω resistors is then used to calculate the impedance seen looking into the amplifier output.
V_IN+
From
50-W
Source
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
49.9 W
49.9 W
V_OUT-
V_OUT+
Open
0.22 mF
To Oscilloscope
with 50-W Input
Figure 56. Slew Rate, Transient Response, Settling Time, Output Impedance, Overdrive Recovery, V_OUT
Swing, and Turn-On/Turn-Off Test Circuit
26
Submit Documentation Feedback
Copyright © 2008–2015, Texas Instruments Incorporated
Product Folder Links: THS4521 THS4522 THS4524