In a 3G/WCDMA mobile handset, the direct conversion receiver (DCR) architecture is commonly used due to its simplicity and low cost, where inter-stage filters are completely eliminated. However the linearity requirement for a direct conversion receiver is very critical. It is essential to define system linearity requirements properly for the receiver to meet the performance requirements. In FDD mode, the transmitter and receiver are continuously working at the same time. The transmitted signal leaks into the receiver due to limited TX to RX isolation of the duplexer and it is possibly the strongest interferer for the receiver in the handset and poses the most stringent linearity requirement for the receiver.
I. 3GPP TEST CASES
A number of test cases are specified in 3GPP for a WCDMA receiver, and each test case has different test conditions. Therefore nonlinearity performance requirements are needed of the receiver in each case. The related test cases are summarized below in Table A-F and are used through out the following discussion.