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3.3 UMTS MODE
3.3.1.1 UMTS RECEIVER (primary Rx)
An antenna switch selects the RF operating band, and then band-specific duplexers filter the incoming Rx
signal while simultaneously routing the transmit signal to the antenna. The duplexer should provide a
differential Rx output.
Each primary receive signal is routed from its duplexer to its MDM LNA through a differential matching
network (MN) that optimizes the power transfer into the gain-stepped LNA. A carefully controlled differential
match is required between the duplexer and the LNA input to maintain the MDM device’s high common-
mode rejection, Tx isolation, out-of-band suppression, and second-order intermodulation performance.
[Figure 3-5] 3G Receiver path
[Figure 3-6] 3G Receiver internal block
The downconverter’s RF circuitry includes a gain-stepped amplifier that supplements the LNA gain steps to
further extend the receiver dynamic range. The quadrature downconverter translates the LNA’s RF signal
directly to baseband, producing two analog output components: in-phase (I) and quadrature (Q). The
baseband signals are routed through multiplexer circuits that only have significance during GSM operation
(see Section 9.6.3); the signals continue to lowpass filters whose passband and stopband characteristics are
programmed for the CDMA waveform. Both filter outputs are buffered and routed to the baseband circuits’
analog-to-digital converters for digitization and further processing.
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