A Study of the Impact of Delay Mismatch on Linearity of Outphasing Transmitters

This paper presents an analytical study of the impact of delay mismatch on the linearity of outphasing transmitters. Analytical expressions are derived to quantify the impact of delay mismatch between the two amplifying paths on the adjacent channel power ratio and error vector magnitude of any complex modulated output signal. These expressions can be used to specify delay mismatch for any given requirement of linearity performance of an outphasing transmitter. A complete LTE transceiver physical layer model in simulink is used to simulate the whole transceiver chain. An embedded model of an outphasing transmitter with a variable delay mismatch is included to compare error vector magnitude simulation data with theoretically derived results for different LTE downlink channels of 1.4 MHz, 10 MHz and 20 MHz channel bandwidths. Outphasing signals are synthesized with different delays and uploaded to a vector signal generator such that adjacent channel power ratios can be measured. This allows for a comparison between hardware-probed results and the theoretical calculations for LTE channels of 1.4 MHz and 10 MHz channel bandwidths.