Dual-tone Method for Phase Linearity Measurement of Wideband Transmitter

Phase linearity is vital for high quality wireless communication, especially for wideband communication. Poor phase linearity will cause poor EVM for transmitter, and then degrade BER performance on the receiver side. That’s why phase linearity is usually required to test for wideband system. In this letter, a method using dual-tone signal to evaluate phase linearity of transmitters with baseband module built in is introduced. For wideband transmitter phase linearity test, it’s difficult to eliminate the phase response of test receiver itself. But it can be mitigated significantly by using this dual-tone method with an assumption that, the phase response of the test receiver’s RF path is nearly linear. To validate this method, a commercial vector signal generator(VSG) was measured as a wideband transmitter. The measurement result has the same level as multi-tone method but with better flatness.