SBOS110C May 1998 – March 2023 OPA2227 , OPA2228 , OPA227 , OPA228 , OPA4227 , OPA4228
PRODUCTION DATA
Figure 7-9 shows the circuit configuration to test the EMIRR IN+. An RF source is connected to the operational amplifier noninverting input terminal using a transmission line. The operational amplifier is configured in a unity gain buffer topology with the output connected to a low-pass filter (LPF) and a digital multimeter (DMM). A large impedance mismatch at the operational amplifier input causes a voltage reflection; however, this effect is characterized and accounted for when determining the EMIRR IN+. The resulting dc offset voltage is sampled and measured by the multimeter. The LPF isolates the multimeter from residual RF signals that can interfere with multimeter accuracy. For more details, see EMI Rejection Ratio of Operational Amplifiers application note.