mm-Wave Mixer-First Receiver With Selective Passive Wideband Low-Pass Filtering

The front-end of a conventional millimeter-wave receiver (RX) consists of a bandpass filter (BPF) and low-noise amplifier (LNA) prior to the frequency down-conversion mixer. In interference-limited wireless channels, it is more footprint and power efficient to remove the BPF and LNA, and realize the mixer as a “passive” switching scheme. The noise figure of this passive mixer-first RX is improved when numerous such RXs are placed in a phased array or multi-input multi-output (MIMO) configuration. The passive switching mixer can be followed with an on-chip selective passive low-pass filter (LPF) with a small footprint given the large channel bandwidth that is typical in mm-wave applications. In this article, system and circuit design aspects of mm-wave passive mixer-first RXs are discussed and validated by a proof-of-concept 65-nm CMOS prototype. The implemented RX operates in the 21-29-GHz frequency range with 0.5-GHz instantaneous single-sideband (SSB) bandwidth, and achieves stopband to passband rejection of >49 dB, an in-band ICP
_{-1 dB}
of -6 dBm, and out-of-band B
_{-1 dB}
> 3.4 dBm.