DCR ( Direct Conversion Receiver )
 
Low-power, high-performance, and low cost integrated RF circuits are common trend of mobile wireless communication. Thus the Direct conversion receiver (DCR) in single chip solution is the best candidate nowadays. The merit of the zero-IF DCR is following, no IF-saw filter, very high integration, and adjustable channel bandwidth; single LO frequency source and feasible multi-mode receiver. However, still it has some demerits such as DC offset component including IM2 component, LO leakage, oscillator pulling by interferer, the imbalance of I and Q path and a flicker noise. Due to these demerits - most unwanted signal is located in a DC band; the low-IF DCR method is suggested. The low-IF overcomes the DC offset problem, a flicker noise, and LO leakage problem because the main signal is not allocated in DC band. But the low-IF DCR still has a problem. To eliminate the image frequency power, it must have very exact I/Q precision - for 40dB Image Rejection Ratio (IIR), 0.1dB and 1 degree mismatch must be achieved. This specification is so tight that the receiver uses the multi-stage poly-phase filter which needs more gain and generates heavy noise. In consideration of these merits and demerits, the short-band receiver such as GSM is suit to the low-IF architecture, but on the other hand, the wide-band receiver such as W-CDMA is suit to the zero-IF architecture.

Implemented W-CDMA Direct Conversion Receiver Block Diagram

LNA

Mixer

IQ Generator

Baseband Block diagram and Filter

VGA

Chip Photograph

Noise Figure of the Receiver

Gain variation and gain step error

Receiver Performance