Block Diagram and Description of Maxim's TDD-WCDMA Transceiver Solution at 1.9GHz
Abstract: This application note presents the block diagram for Maxim's TDD-WCDMA transceiver solution. The direct conversion receiver eliminates one SAW filter. Fast DC offset cancellation supports fast settling time. The operating frequency range is 1900MHz to 1920MHz. The transmitter achieves EVM of better than 7.5%.
Overview
TDD-WCDMA (time division duplex-wideband code division multiple access) is the third-generation (3G) cellular phone standard adopted by 3GGP. Several frequency bands, such as 2.0GHz, 1.9GHz, and 800MHz, have been assigned for these applications.
Since TDD-WCDMA employs time division duplexing and no Tx-Rx (transmit-receive) frequency separation is required, it makes the frequency band's availability much more flexible in spectrum-limited areas.
In the radio section of the handset, the TDD-WCDMA radio requires fast settling time, high dynamic range, low current consumption, and high linearity in both the transmitter and receiver sections. Maxim's zero-IF chipset delivers the highest performance, the smallest implementation size, and the least expensive radio solution available in the TDD-WCDMA handset market. The Figure 1 block diagram shows a typical application.
Figure 1.
Transmitter
The MAX2395 is a fully monolithic quasi-direct modulator IC for use in WCDMA/UMTS transmitters. The quasi-direct modulation architecture reduces system cost, component count, and board space compared to transmitters using IF SAW filters, IF VCO and IF synthesizer blocks. It includes I/Q baseband filters, an IF I/Q modulator with VGA, a fully monolithic VCO with PLL, an upconverting mixer with VGA, and a power amplifier driver. It is the ideal transmitter for TDD-WCDMA because of these features:
Frequency range: 1900MHz to 1920MHz
Output Power of +8dBm with -45dBc ACPR
82dB (min) Power-Control Range
On-Chip RF PLL, with Fully Monolithic VCO and Tank
30dBc (min) Carrier Suppression
35dBc (min) Sideband Suppression
No Need for IF SAW Filter
EVM ≤ 7.5% for POUT: +8dBm to -44dBm
Low-Noise Power During the Power-Down Mode
Offered in Leadless, 5mm × 5mm, 28-Pin QFN Package
Power Amplifier
To improve efficiency at medium output power, the PA power supply, VCC_PA, is driven at reduced voltage using a low-dropout switching regulator, the MAX1821.
Receivers
The MAX2393 is a fully integrated direct-conversion receiver for 3GPP TDD-WCDMA applications. It provides a complete receiver solution from antenna to baseband I&Q outputs, eliminating the use of an off-chip IF SAW filter and of external Rx LO generation and synthesis. In the MAX2393, channel bandwidth selection (1.92MHz/0.64MHz) is done on-chip electronically. It consists of an ultra-low current LNA with on-chip output matching and two-step gain modes. The zero-IF demodulator has a differential circuit topology for best input IP2 and for minimum LO leakage to receiver's input. The channel selectivity is done completely in the baseband section of the receiver with an on-chip low-pass filter. The DC-offset cancellation in the I/Q baseband channels is done fully on-chip using a DC servo loop connected over the AGC section. For large DC-offset transients, very fast settling time is obtained by automatic optimization of the time-constant of the DC-offset cancellation circuit. The key features of the MAX2393 are as follows:
Frequency Range: 1900MHz to 1920MHz
Low Operating Supply Current: 33mA at High-Gain Mode
NF (Noise Figure, in High-Gain Mode): 3.0dB DSB (Double Side Band)
On-Chip RF PLL, with Fully Monolithic VCO and Tank
High Dynamic Range: Over 90dB of Gain Control
Voltage Gain (High-Gain Mode): 100dB
Input IP3 (High-Gain Mode): -16.5dBm
Input IP2 (High-Gain Mode, 15MHz Offset): +22dBm
LO Leakage (at LNA Input): -74dBm, (max)
No Need for IF SAW Filter
Adjacent Channel Selectivity: 55dB
No Need for IF SAW Filter and Off-Chip RF VCO Module + PLL Synthesizer
Offered in Leadless, 5mm × 5mm, 28-Pin QFN Package
Automatic Updates
Would you like to be automatically notified when new application notes are published in your areas of interest? Sign up for EE-Mail™.
Download, PDF Format
