SLOS358C September 2011 – April 2020 THS4531
The circuit shown in Figure 67 is used to measure the frequency response of the amplifier.
A network analyzer is used as the signal source and the measurement device. The output impedance of the network analyzer is 50-Ω and is DC coupled. RIT and RG are chosen to impedance match to 50 Ω and maintain the proper gain. To balance the amplifier, a 49.9 Ω resistor to ground is inserted across RIT on the alternate input.
The output is routed to the input of the network analyzer via 50 Ω coax. For 2 k load, 37.9 dB is added to the measurement to refer back to the amplifier’s output per Table 4.
For output impedance, the signal is injected at VOUT with VIN left open. The voltage drop across the 2x RO resistors is measured with a high impedance differential probe and used to calculate the impedance seen looking into the amplifier’s output.