THS4541-Q1 Datasheet, PDF (44/60 Pages) Texas Instruments – 850-MHz Fully Differential Amplifier

THS4541-Q1
SLOS930A – NOVEMBER 2015 – REVISED NOVEMBER 2015
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
The THS4541-Q1 offers an effective solution over a broad range of applications. Two examples are developed
here. First, an attenuator stage that directly receives a higher input signal voltage and translates it to a lower
differential swing on a fixed common-mode is shown. This design requires some attention to frequency-response
flatness issues, and one approach to managing these issues is shown. The second example is a gain of 2 V/V,
matched input of 50 Ω to an output set to 0.95 V common-mode followed by a third-order Bessel filter with
approximately 20 MHz of bandwidth feeding into the ADC34J22, a low-power, 12-bit, quad 50-MSPS JESD 204B
ADC.
10.2 Typical Applications
10.2.1 Designing Attenuators
Vcc
+ _Vcc
± 5V
Gain of 0.1 V/V from Rg1,
Single-Ended to Differential,
DC-Coupled, Single Supply
THS4541 Wideband,
Fully-Differential Amplifier
Rf1
402
Vcm
+ _Vcm
± 2.5 V
Rg1
4.02 k
+
VG1
±
Vocm
Vcc
±
+
FDA
±
+
PD
R1
+
500
VM1
±
Rg2
Vcc
4.02 k
Rf2
402
Figure 77. Divide-by-10 Attenuator Application for the THS4541-Q1
10.2.1.1 Design Requirements
In this design, the aim is to:
1. Present a 4-kΩ input impedance to a ±40-V input signal (maximum ±10 mA from the prior stage).
2. Attenuate that swing by a factor 1/10 (–20 dB) to a differential output swing.
3. Place that swing on a 2.5-V common-mode voltage at the THS4541-Q1 outputs.
4. Operate on a single +5-V supply and ground.
5. Tune the frequency response to a flat Butterworth response with external capacitors.
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