Specifications

TC35 / TC37 Hardware Interface Description
TC35_37_HD_02_V03.10 - Released Page 56 of 92 21.12.2001
4 Radio interface
The RF part of TC35 and TC37 is based on the Transceiver Chip SMARTi. The transceiver
consists of a heterodyne receiver part, an upconversion modulation loop transmitter, a RF
PLL and fully integrated IF synthesizer.
4.1 Receiver
The receiver section of RF part provides the following features:
• Two low noise RF mixers for optimal dual band architectures
• Programmable Gain IF/Baseband amplifier strip by steps of 2dB
• Quadrature IF demodulator
• Differential I and Q outputs
• Programmable output DC level
• Automatic DC offset compensation
The signal received from the antenna first passes a gain programmable discrete low noise
amplifier (LNA) in the receiver chain. After external filtering the double balanced RF signal is
down converted to an intermediate frequency (IF) by a first mixer. The IF signal is passed
through an external Surface Acoustic Wave (SAW) filter, which performs a rough channel
selection. After that the signal is fed again into the receiver circuit to pass a digitally
programmable gain-controlled amplifier (PGC). Finally the amplified IF signal is demodulated
to baseband by a IQ demodulator. A differential offset introduced by the IQ demodulator is
compensated by a sample-and-hold circuit. The resulting differential I and Q baseband
signals are converted independently from analog to digital forming two 6.5Mbit/s data
streams.
4.2 Transmitter
The transmitter section of the RF part provides the following features:
• Differential I and Q inputs
• IF quadrature modulator
• Integrated IF filters and down conversion mixer
• Digital 250MHz Phase Frequency Detector
• Programmable Charge pump current and phase detector polarity
The digital 10-bit I and Q baseband components (GMSK modulated and 8-times
oversampled) provided by GSM baseband processor are converted in parallel from digital to
analog. The resulting analog differential baseband signal is fed to the input of a quadrature
amplitude modulator followed by the up-conversion loop. This up-conversion loop
configuration converts the IF-band signal to the desired radio frequency in the 900MHz or
1.8GHz band. Finally a RF power module (Dual band) amplifies the RF signal to the required
power. Ramping of the power amplifier is performed software controlled by 10-bit control
values.