A 1.9 GHz Si direct conversion receiver IC for QPSK modulation systems

This paper presents a possible BiCMOS solution for a direct conversion receiver (DCR) for QPSK communication systems such as personal handy-phone system (PHS). DCR chips reported are for constant-amplitude modulation systems such as FSK or GMSK. However, no DCR chip for QPSK systems has been reported yet,because a 2nd-order nonlinearity often strongly deteriorates a receiver sensitivity for QPSK systems. That is, amplitude modulation components in QPSK are converted down into spurious baseband signals, while FSK and/or GMSK systems do not suffer from 2nd-order nonlinearity. A DCR chip including an LNA is fabricated for a feasibility study of DCR for QPSK systems.