Evaluation board description

AN2705

4/8

If you connect a system with an input impedance other than 75

Ω to the PCB output, a Π

resistor footprint on the board allows you to match impedances.

For example: you connect a scope with a 50

Ωoutput impedance. To match impedances, you

must add the following resistors: R5=2.2k

Ω, R6=130Ω, R7=82Ω

The output can be AC or DC connected with this configuration.

Figure 5.

TSH173 output impedance matching

Power supply

Correct power supply bypassing is very important for optimizing performance. A 10µF and a

100nF are soldered on the board. This gives good performance. However, you can improve

it by adding a 100µF capacitor in C3 and placing a 560µH coil instead of the zero ohm

resistor in LR1.

Figure 6.

Power supply