Electronic Design

Direct-Conversion 2.4-GHz Transceiver Chips Epitomize Design Reuse

Apair of 2.4-GHz transceivers from Maxim Integrated Products exemplifies state-of-theart design reuse in RF ICs. These zero-IF, RF transceiver chips both provide an RF-to-baseband receive path, baseband-to-RF transmit path, voltage- controlled oscillator (VCO), frequency synthesizer, crystal oscillator, and baseband/ control interface.

The MAX2830 adds an RF power amplifier (PA) rated at 17.1 dBm and a transceive and antenna diversity switch. It targets IEEE 802.11g and b Wi-Fi applications. The MAX2837, which delivers 0 dBm to drive an external PA, primarily suits WiMAX, WiBro, and 4G cellular applications. With either IC, applications only externally need an RF bandpass filter (BPF), crystal, and a small number of passive components.

The chips use a sigma-delta fractional-N RF synthesizer with resolution finer than 20 Hz, but there is a difference in implementation. In the MAX2830, the synthesizer includes a divide-by-1 or a divide-by-2 reference frequency divider (see the green areas in the figure). The MAX2837 does not. In the data sheets for both parts, the MAX2830 lists closed-loop phase-noise values, and the MAX2837 does not.

A digitally tuned crystal oscillator permits the use of a low-cost crystal in place of a temperature-compensated crystal oscillator. The transceiver IC also integrates circuits for on-chip dc offset cancellation, I/Q error, and carrier-leakage detection circuits. And, both ICs have on-chip monolithic filters for both the receiver and transmitter, eliminating the need for external surface-acousticwave (SAW) filters.

In the MAX2830, those baseband filters are optimized for the IEEE 802.11g standard and proprietary turbo modes up to 40- MHz channel bandwidth, suiting them for the full range of 802.11g orthogonal frequency-division modulation (OFDM) data rates (6 to 54 Mbits/s) and 802.11b quadrature phaseshift keying (QPSK) and complementary code keying (CCK) data rates (1 to 11 Mbits/s).

The filters in the MAX2837 support up to 2048-carrier fast Fourier transform (FFT) OFDM and implement programmable channel filters for 1.75- to 28-MHz RF channel bandwidths. Including frequency transient settling, the transceiver requires 2- μs TX-RX switching time.

The transceiver portion of the MAX2830 operates from 2.7 to 3.6 V, and its PA operates from 2.7 to 4.2 V. It comes in a 7- by 7- mm, leadless 48-pin TQFN-EP package. Lacking the PA, the MAX2837 operates from a single 2.7- to 3.6-V supply and comes in a 6- by 6-mm, leadless, 48-pin TQFN package. The ICs are built on Maxim's proprietary silicon-germanium biCMOS process.

The MAX2830 starts at $5.97, and the MAX2837 starts at $8.38, both in lots of 1000 and up. Evaluation kits are available.

Maxim Integrated Products www.maxim-ic.com

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