Reduction of electrical baseband memory effect in high-power LDMOS devices using optimum termination for IMD3 and IMD5 using active load-pull

The usual approach in minimizing electrical memory in PA design is to terminate base-band impedances into a broadband short circuit, usually provided in the form of an array of bypass capacitors attached close to the output terminal of the device. This paper investigates the validity of this approach and compares linearity performance under different IF impedance terminations. Active IF load-pull is used as a modulation-frequency independent means of engineering the significant low-frequency IF voltage components generated as a result of two-tone excitation. Selective IF loads are presented in order to probe device linearity as a function of IF impedance. One significant observation is the existence of specific IF loads that result in the suppression of both IM3 and IM5 intermodulation components by more than 16dB and 10dB respectively, in comparison to the case of a conventional IF short termination. These investigations are performed using a 20W LDMOS device characterised at 2.1 GHz within a purpose built, high-power measurement system.