THS4541_15 Datasheet, PDF (46/61 Pages) Texas Instruments – THS4541 Negative Rail Input, Rail-to-Rail Output, Precision, 850-MHz Fully Differential Amplifier

THS4541
SLOS375A – AUGUST 2014 – REVISED SEPTEMBER 2014
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Typical Applications (continued)
The 1 pF across the inputs is really a total 1.85 pF, including the internal differential capacitance, and a Cs =
3.7 pF for a single-ended design from Equation 17.
These two designs (with and without the capacitors) were both bench tested and simulated using the THS4541
TINA model giving the results of Figure 79.
This method does a good job of flattening the response for what starts out as a low phase-margin attenuator
application. The simulation model does a very good job of predicting the peaking and showing the same
improvement with the external capacitors; both giving a flat, approximately 250-MHz, closed-loop bandwidth for
this gain of a 0.1-V/V design. In this example, the output noise begins to peak up (as a result of the noise-gain
shaping of the capacitors) above 70 MHz. Use postfiltering to minimize any increase in the integrated noise using
this technique. Using this solution to deliver an 8-V_PP differential output to a successive approximation register
(SAR) ADC (using the 2.5-V Vocm shown), the circuit accepts up to ±40-V inputs, where the 4-kΩ input Rg1
draws ±10 mA from the source.
10.2.1.3 Application Curve
-11
-14
-17
-20
-23
-26
-29
-32
1M
Bench without caps
Bench with caps
Sim without caps
Sim with caps
10M
100M
Frequency (Hz)
1G
D064
Figure 79. Attenuator Response Shapes with and without External Compensation
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