THS4520_14 Datasheet, PDF (20/37 Pages) Texas Instruments – WIDEBAND, LOW NOISE, LOW DISTORTION FULLY DIFFERENTIAL AMPLIFIER

THS4520
SLOS503B – SEPTEMBER 2006 – REVISED JULY 2007
of the network analyzer is 50 Ω. R_IT and R_G are
chosen to impedance match to 50 Ω, and to 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.
The output is probed using a high-impedance
differential probe across the 100-Ω resistor. The gain
is referred to the amplifier output by adding back the
6-dB loss due to the voltage divider on the output.
From ^VIN
50 W
Source
RG
RIT
0.22 mF
49.9 W
RG
RIT
RF
V_S+
THS4520
CM
V_S−
49.9 W
49.9 W ^{100 W}
Open
0.22 mF
Output Measured
Here With High
Impedance
Differential Probe
RF
Figure 56. Frequency Response Test Circuit
S-Parameter, Slew Rate, Transient Response,
Settling Time, Output Voltage
The circuit shown in Figure 57 is used to measure
s-parameters, slew rate, transient response, settling
time, and output voltage swing.
Because S21 is measured single-ended at the load
with 50-Ω double termination, add 12 dB to see the
amplifier’s output as a differential signal.
www.ti.com
From ^VIN
50 Ω
Source
RG
R IT
0.22 mF
49.9 W
RG
R IT
RF
V_S+
THS4520
CM
V_S−
RF
49.9 W
49.9 W
Open
0.22 mF
V_{OUT+ To 50 W}
Test
V_OUT− ^Equipment
Figure 57. S-Parameter, SR, Transient Response,
Settling Time, V_OUT Swing
CM Input
The circuit shown in Figure 58 is used to measure
the frequency response of the CM input. Frequency
response is measured single-ended at V_OUT+ or
V_OUT– with the input injected at V_IN, R_CM = 0 Ω and
R_CMT = 49.9 Ω.
0.22 mF
49.9 W
0.22 mF
49.9 W
RG
RIT
RG
RIT
RF
VS+
49.9 W
THS4520 _{49.9 W}
CM
VS–
RF
RCM
RCMT
VOUT–
To
50-W
Test
VOUT+ _Equipment
VIN From
50-W
Source
Figure 58. CM Input Test Circuit
20
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