A 1.9GHz direct conversion receiver(DCR) chip which integrates an LNA, I/Q mixers(MIX), active lowpass filters(LDF) and variable gain amplifiers(VGA) was fabricated. Because the DCR for QPSK modulation systems is sensitive to the 2nd-order nonlinearity, linearization techniques are adopted in MIX and LPF. The DCR chip was fabricated using a BiCMOS process, and the die size is 5.1 mm by 5.1mm. The chip can operate from 2.7 V supply voltage and consumes 165mW when all the functions are activated. Suppression of local signal radiation and the 2nd-order distortion indicate the feasibility of Si-based DCR for QPSK modulation systems such as PHS.

A novel adder-free architecture for realizing a small-size π/4-shift QPSK signal generator IC is presented. In order to realize an adder function, analog current-mode addition is utilized instead of digital adders. Impulse responses of a roll-off filter are stored in a ROM as a Δ-Σ modulated one-bit data stream. This can greatly reduce the die size to 0.8mm 0.8mm while maintaining high modulation accuracy. The test chip was fabricated by using the standard 0.8µm CMOS technology, and the chip achieved 1.8% vector modulation error with a 2.7V power supply.