THS4561 Datasheet, PDF (24/35 Pages) Texas Instruments – Low-Power, High Supply Range, 70-MHz, Fully Differential Amplifier

THS4561
SBOS874 – AUGUST 2017
10 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
Most applications for the THS4561 strive to deliver the best dynamic range in a design that delivers the desired
signal processing along with adequate phase margin for the amplifier itself. The following sections detail some of
the design issues with analysis and guidelines for improved performance.
10.1.1 Differential Open-Loop Gain and Output Impedance
The most important elements to the closed-loop performance are the open-loop gain and open-loop output
impedance. Figure 7 and Figure 8 show the simulated differential open-loop gain and phase from the differential
inputs to the differential outputs with no load and with a 100-Ω load. Operating with no load removes any effect
introduced by the open-loop output impedance to a finite load. This A_OL simulation removes the internal feedback
capacitors to isolate the forward path gain and phase (see ). The internal capacitance becomes part of the
feedback network that sets the noise gain and phase combined with the external elements. The simulated
differential open-loop output impedance is shown in Figure 9.
70
60
Aol no load
Aol 100 : load
50
40
30
20
10
0
-10
-20
-30
-40
-50
100k
1M
10M
100M
1G
Frequency (Hz)
Figure 7. No-Load and 100-Ω Loaded A_OL Gain
10000
0
Aol phase no load
Aol phase 100 : load
-50
-100
-150
-200
-250
-300
100k
1M
10M
100M
1G
Frequency (Hz)
Figure 8. No-Load and 100-Ω A_OL Phase
1000
100
10
10 100 1k 10k 100k 1M 10M 100M 1G
Frequency (Hz)
Figure 9. Differential Open-Loop Output Impedance
24
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