THS4552 Datasheet, PDF (24/71 Pages) Texas Instruments – Dual-Channel, Low-Noise, Precision, 150-MHz, Fully Differential Amplifier

THS4552
SBOS831 – DECEMBER 2016
www.ti.com
Example Characterization Circuits (continued)
Starting from the test circuit of Figure 61, various elements are modified to show the effect of these elements
over a range of design targets, specifically:
• The gain setting is changed by adjusting the R_T and the two R_G elements to provide a 50-Ω input match and
setting the feedback resistors to 1 kΩ.
• Output loading of both resistive and capacitive load testing. Changing to lower resistive loads is accomplished
by adding parallel resistors across the output pins in Figure 61. Changing to capacitive loads adds series
output resistors to a differential capacitance before the 1-kΩ sense path of Figure 61.
• Power-supply settings. Most often, a single 5-V test uses a ±2.5-V supply and a 3-V test uses ±1.5-V supplies
with the V_OCM input control at ground.
• The disable control pin (PD) is tied to the positive supply (V_S+) for any active channel test.
8.2 Output Interface Circuit for DC-Coupled Differential Testing
The pulse response plots were taken using the output circuit of Figure 64. The two sides of this circuit present a
500-Ω load to ground (for a differential 1-kΩ load) with a 50-Ω source to the two scope inputs. Trace math is
used to combine the two sides into the pulse response plots of Figure 7 to Figure 10 and Figure 25 to Figure 28.
Using balanced bipolar supplies for this test ensures that the THS4552 outputs deliver a ground-centered
differential swing. This setup produces no dc load currents using the circuit of Figure 64.
RO1
475
THS4552
Output
RO2
475
RM1
56.2
50-
Scope
Input
RM1
56.2
50-
Scope
Input
Copyright © 2016, Texas Instruments Incorporated
Figure 64. Output Interface for DC-Coupled Differential Outputs
8.3 Output Common-Mode Measurements
The circuit of Figure 65 is a typical setup for common-mode measurements.
THS4552 Wideband,
Fully Differential Amplifier
RG1
1k
RF1
1k
Signal
Source
RS
49.9
VOCM
Input
RT
49.9
RT
1k
VS+
±
+
FDA
±
+
PD
VS- ^VS+
100
50-
Measurement
Equipment
100
RF2
1k
Copyright © 2016, Texas Instruments Incorporated
Figure 65. Output Common-Mode Measurements
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