Texas Instruments THS4211 Evaluation Module THS4211EVM THS4211EVM データシート

3-2

If the user provides an external load, R7 may be removed, and R6 replaced
with a 0-

Ω

 jumper. The EVM then provides a gain of 2 (6 dB) at the output

connector J4. A gain of 2 is often used to compensate for the voltage division
effect when series and termination resistors are used for stage impedance
matching.

The default configuration of the EVM is a noninverting gain stage with a voltage
divider on the output. If a gain of 2 is desired, the user should change R6 to
0 

Ω

, and remove R7 as shown in Figure 3-2:

  

  

  

Power supply decoupling not shown.





Gain for this circuit is:

V

O

V

I

+

1

)

R5
R3

for R2 = 0, when the input voltage is measured at J2.

Changing R6 to 49.9 

Ω

 in this and the subsequent section, allows the EVM to

connect to a 50-

Ω

 load. This amplifier is designed to attain optimum

performance driving 500-

Ω

 loads, but also drives 100-

Ω 

loads—refer to data

sheet characteristics.

The unity gain noninverting buffer configuration can be implemented by re-
moving R3 and R2. This configuration, however, requires a 392-

Ω

 

resistor

to be installed in location R5 on the EVM. A resistor less than the recom-
mended value may cause the EVM to become unstable due to inductance
on the PCB trace. Texas Instruments manufactures a different EVM for cus-
tomers who wish to evaluate the noninverting buffer configuration. This EVM
is optimized for low inductance traces on the op amp output. It is implement-
ed on THS4211EVM-UG.