Service Manual

1. Overview
IRT3000 receives modulated digital signals from the MSM of the digital circuit and then, changes them into analog
signals by the digital/analog converter (DAC, D/A Converter) in order to create baseband signals. Created baseband
signals are changed into IF signals by IFT3000 and then, fed into the Mixer after going through AGC. IF signals that
have been fed are mixed with the signals of VCO and changed into the RF signals and then, they are amplified at the
Power AMP. Finally, they are sent out to the cell site via the antenna after going through the isolator and duplexer.
2. RF Transmit / Receive Part
2.1 CDMA Transmit End
8 bit I and Q transmit signals are inputted into 2 DACs (DIGITAL-TO-ANALOG CONVERTER) from the output
terminal TX_IQDATA0 ~ TX_IQDATA7 of MSM through the input terminals TXD0~TXD7 of BBA. Transmit
signal input speed is two times of TXCLK+, TXCLK- which are two transmit/receive reference frequency.
Among transmit signals being inputted, signals are inputted into I signal DAC when the transmit clock is in the rise
edge, whereas signals are inputted into Q Signal DAC during the drop edge. I and Q transmit signals are
compensated and outputted at MSM in order to compensate the 1/2 clock time difference generated between
reference clocks. In the signals coming out from the output terminal of DAC, there are spurious frequency
ingredients resulting from DAC output transition edge and parasite ingredients, transmit clock frequencies and
harmonics which are unwanted signals. Accordingly, spurious ingredients are removed by passing the signals
through LPF of passband 6.30KHz. Unlike the receive end, the transmit end LPF requires no OFFSET adjustment.
Analog baseband signals that have passed the CDMA LPF are mixed with I and Q signals of frequency 130.38 MHz
(260.76 MHz created in the BBA internal VCO are divided by half into frequency 130.38MHz having the phase
difference of 90 degrees) in two mixers. The mixed signals are added again and converted into IF frequency 130.38
MHz
±
630 KHz (CDMA Spread Power Density Modulated Signals) and then, outputted.
2.2. Tx IF/Baseband Processors, IFT3000 (U105)
The IFT3000 includes digital-to-analog converters(DAC) for converting digital baseband to analog baseband, low-
pass filters, a mixer for up-converting to IF and an 85 dB dynamic range Tx AGC amplifier. The IFT3000 includes
a fully programmable phase-locked loop(PLL) for generating Tx LO and IF frequencies. The IFT3000 also has an 8-
bit general purpose ADC with three selectable inputs for monitoring battery level, RF signal strength and phone
CHAPTER 3. Circuit Description