Block diagram of TD-SCDMA wireless chipset for mobile phones
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China's choice for 3G cell phones is the TD-SCDMA system. This article presents a detailed block diagram of a cell phone transceiver, in which the MAX2361 is the transmitter IC, the MAX2291 is the power amplifier (PA), the MAX2388 and MAX2309 form the receiver, and a VCO buffer amplifier provides good isolation to maintain a clear LO signal.
introduction TD-SCDMA is the third generation (3G) cellular phone standard currently being developed in China. In November 1999, the TD-SCDMA standard was adopted by the International Telecommunication Union as one of the 3GPP mobile communication standards. In order to increase channel capacity and improve bandwidth efficiency, TD-SCDMA combines time division duplex (TDD) with CDMA by utilizing uplink (reverse link) synchronization, software radio and smart antenna technologies. In the RF part of the mobile phone, TD-SCDMA requires fast switching time, high dynamic range, and high linearity in the transmitter and receiver parts. Maxim's chipset can provide the highest performance, smallest structure size, and most affordable wireless solution in the TD-SCDMA mobile phone market. The following block diagram introduces a typical application. Transmitter The MAX236X is a complete quadrature transmitter consisting of a quadrature modulator, variable gain IF and RF amplifiers, an image rejection upconverter, a dual RF and IF synthesizer, and a dual-band power amplifier (PA) driver. The MAX236X is ideal as a TD-SCDMA transmitter due to the following features: - The output power is +8dBm with excellent ACPR specification
- 100dB power control range
- Double integer division IF and RF synthesizer
- An image rejection upconverter that eliminates the need for a SAW filter
- Power consumption current decreases as RF output power decreases
- In power down mode, there is low noise power
- 48-pin QFN package, 7mm×7mm
Power Amplifier The MAX229X is an optimized linear amplifier for TD-SCDMA applications. It provides +26dBm output power with 30% power efficiency (PAE) and 37dBc ACLR1. Receiver The MAX2388 consists of a low-noise amplifier (LNA), a downconverter, and a local oscillator (LO) buffer amplifier. Because it consumes very low current (9.9mA), it is ideal for TD-CDMA applications. The low-noise amplifier provides fixed gains of 15dB and -3dB, while having a 1.7dB noise figure and +4.2dBm input IIP3 in high-gain mode. The mixer is also optimized to have high linearity and low noise performance at both gain levels. Even with 3dB filter insertion loss, the noise figure of the entire cascade is as low as 2.3dB. The LO buffer provides excellent isolation and sufficient amplification. This feature enables the system to use a single RF-LO to drive both the transmitter and the receiver. The MAX2388 uses an ultra-small 12-pin QFN package that measures only 3mm x 3mm. The MAX2309 is an IF receiver designed for single-frequency, single-mode, CDMA-based cellular phone systems. The input frequency range is optimized for 70MHz to 300MHz. A variable-gain amplifier (VGA) and an I/Q demodulator complete the signal path. The device features guaranteed +2.7V operation, more than 110dB of dynamic range, and high input IP3 (-33dBm at 35dBm gain, +1.7dBm at -35dBm gain). In addition to demodulation, the MAX2309 includes an oscillator, a synthesizer, and an LO buffer to form an autonomous IF subsystem. This device will enable the IF-LO to drive the transmitter's modulator. The MAX2309 is available in a 28-pin QFN package measuring only 5mm x 5mm. The MAX2472 is a dual-channel VCO buffer amplifier with high isolation performance. The optimized frequency range is 500MHz to 2500MHz. The high isolation performance (49dB) greatly reduces the pulling of the transmitted modulation signal on the VCO frequency. The MAX2472 also has a shutdown pin, making it suitable for TDD systems such as TD-SCDMA. 
TD-SCDMA/GSM Dual Mode Transceiver Reference Design Block Diagram, Rev. A
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