Functional Description - Panasonic EB-G450 Technical Manual

TRANSMITTER

4.2

The main building block in the Tx line-up is the transmitter IC U103 which provides a Class 4 (2Watts) transmitter.

Figure 1: Transmitter IC U103

450-0401

The RF mixer is used to generate the GSM carrier, which is then modulated by the baseband I-Q signals in the

quadrature modulator. The output from the quadrature modulator is buffered and is output differentially at about -

8dBm.

The RF LO is obtained from the same VCO that supplies the Rx LO. Therefore, the Tx IF frequency is 45MHz

greater than the Rx IF frequency. The IF LO is generated by the same discrete VCO as the Rx IF VCO offset by

90MHz. The VCO frequency is divided by two by an on-chip divider to generate the required 246MHz.

The output from Tx IC is filtered before and after the PA driver U106. The amount of filtering provided ensures that

the Tx spurii and the Tx noise in the Rx band are within GSM limits with sufficient margins.

The PA amplifies the output from the PA driver to any required level up to PL5 (33dBm) at the antenna. The power

level can be controlled as required in Phase II GSM in 2dB steps from 33dBm to 9dBm. To achieve the accuracy

and time mask requirements for the output power, a closed loop power control design has been implemented. In

this method, a portion of the output power is coupled into a detector. This sample is then compared with a ramp

waveform whose rising and falling edges are precisely shaped to ensure that the frequency splash due to the fast

turn on and off of the PA remains in specifications. The level of the ramp waveform determines output power level

that needs to be transmitted.

The output from the PA is filtered through a discrete low-pass filter to ensure that there is sufficient margin in the

rejection of the second and third Tx harmonics as the duplexer rejection is not sufficient.

For a typical output power of 33dBm at the antenna, assuming a typical loss of 1.5dB between the PA output and

the antenna. The PA has an efficiency minimum of 40%.

Issue 1

Section 4

MCUK971001G8

Revision 0

4 - 2

Technical Guide

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