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What is Direct-conversion receiver?

A receiver architecture (zero-IF) that sets the local oscillator (LO) to the received frequency and converts directly to baseband without an intermediate frequency, using two mixers for the in-phase (I) and quadrature (Q) components. It needs no image-reject or IF filters and is easy to integrate on one CMOS chip. On the other hand, it needs countermeasures against the DC shift (DC offset) caused by LO leakage, 1/f noise and I/Q imbalance.

Japanese name: ダイレクトコンバージョン方式

Direct-conversion receiver appears in 1 practice question across 1 topic, including Wireless Communication Basics.

Field: Wireless Communication Basics

Try it: questions about Direct-conversion receiver

Which describes a direct-conversion receiver, which sets the local oscillator (LO) to the same frequency as the received signal and converts directly to baseband without an intermediate frequency, compared with a superheterodyne receiver?

  1. ABecause it uses no intermediate frequency, the image frequency problem becomes worse and a high-performance image-reject filter is required
  2. BBecause it converts frequency two or more times, the circuit is complex and hard to integrate on a CMOS chip
  3. CIt needs no external IF filter and is easy to integrate, but it is susceptible to a DC shift (DC offset) caused by LO leakage mixing with itself and to low-frequency 1/f noise
Show answer and explanation

Answer: C. It needs no external IF filter and is easy to integrate, but it is susceptible to a DC shift (DC offset) caused by LO leakage mixing with itself and to low-frequency 1/f noise

A direct-conversion receiver (zero-IF receiver) tunes the LO to the received frequency and converts directly to baseband with two mixers, in-phase (I) and quadrature (Q). The two I and Q paths distinguish positive and negative frequencies, so there is no problem of an image signal at another frequency getting in and no IF filter is needed, making it easy to integrate on one CMOS chip; it is widely used in transceivers for mobile phones and other devices. On the other hand, when the LO signal leaks toward the antenna and mixes with itself, a DC component (DC offset) arises that is hard to distinguish from the baseband signal. Also, because the converted signal lies near DC, it is susceptible to transistor 1/f noise and to mismatch between the I and Q paths (IQ imbalance).

Direct-conversion receiver in the explanations

Questions that mention Direct-conversion receiver (1)

  1. Which describes a direct-conversion receiver, which sets the local oscillator (LO) to the same frequency as the received signal and converts directly to baseband without an intermediate frequency, compared with a superheterodyne receiver?

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Related terms

Superheterodyne receiver CMOS 1/f noise (flicker noise) Beamforming Bluetooth Low Energy (BLE) Fading Free-space path loss (FSPL) Hidden node problem Link budget LPWA (low-power wide-area)

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