THS4541IRUNR.B datasheet(22/66 Pages) TI2

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Figure 7-1 shows the starting selections for the frequency domain characterization curves. Then, various

elements are modified to show the impact over a range of design targets, specifically:

• Gain setting is changed by adjusting Rt and the 2 – Rg elements (holding a 50-Ω input match).

• Output loading, including both resistive and capacitive load testing.

• 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.

• The disable control pin is tied to Vs+ for any active channel test.

Because most network and spectrum analyzers are a single-ended input, the output network on the THS4541

characterization tests typically show the desired load connected through a balun to a single-ended, 50-Ω load,

while presenting a 50-Ω source from the balun output back into the balun. For instance, Figure 7-2 shows a

wideband MA/Com balun used for Figure 7-1. This network shows a 500-Ω differential load to the THS4541,

but an ac-coupled, 50-Ω source to the network analyzer. Distortion testing typically uses a lower-frequency,

dc-isolated balun (such as the TT1-6T) that is rotated 90° from the wider band interface of Figure 7-2.

Ro1

237

100 nF

Ro2

237

56.2

C10

100 nF

50-

Load

ETC1-1-13

500-

Differential

Load

THS4541

Output

Figure 7-2. Example 500-Ω Load to a Single-Ended, Doubly-Terminated, AC-Coupled, 50-Ω Interface

This approach allows a higher differential load, but with a wideband 50-Ω output match at the cost of

considerable signal-path insertion loss. This loss is acceptable for characterization, and is normalized out to

show the characterization curves.

Figure 7-3 shows the circuit that is used as a starting point for time-domain or dc-coupled testing, where the gain

of a 5 V/V setting used in Figure 6-25 and Figure 6-27 are illustrated.

Rf1

402

500

Rg1

68.1

Rg2

100

80.6

Output

Measurement

Point

THS4541 Wideband,

Fully-Differential Amplifier

Rf2

402

50-

Input Match,

Gain of 5 V/V from Rt,

Single-Ended Source to

Differential Step-Response Test

50-

Source

Vcc

Vocm

Vcc

FDA

Figure 7-3. DC-Coupled, Single-Ended-to-Differential, Basic Test Circuit Set for a Gain of 5 V/V

THS4541

SLOS375B – AUGUST 2014 – REVISED FEBRUARY 2024

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