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PMB2240

GSM-Transmitter

Siemens AG 

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The GSM transmitter PMB2240 contains a number of functions that have been realised with multiple

chips earlier:

- Oscillator signal input balanced or unbalanced

- RF-PLL prescaler

- IF-PLL dividers and phase detection

- TX - mixer

- I/Q modulator

The PMB2240 V1.6 is designed to be used with an external RF oscillator module. On chip this signal is

AC-coupled to an internal buffer stage. Therefore the RF input is suitable for symmetrical or single

ended use. There is no need for an external DC-bias of the RF input. The active parts of the IF

oscillator are located on the receive chip PMB2405.

A buffer BufRX, which can be powered down by pin PDBUFRX, is used to transmit the RF oscillator

signal to the receiver chip to drive the RF receive mixer. A special input buffer BufTX receives the IF

oscillator signal from the receive chip or an external source.

The RF oscillator signal is divided by the integrated 64/65 prescaler which can be connected to the

CMOS PLL circuit PMB2306 for the RF oscillator PLL. The supply pin VCCPR is a separate prescaler

supply, which openes the possilility to run the prescaler and the rest of the RF synthesizer on a supply

voltage that is different from the supplies of the rest of the chip.

For the IF-PLL the active oscillator structures on the PMB2405 or an external VCO module can be

used. The PMB2240 V1.6 contains the digital parts tor the IF oscillator PLL (fixed-PLL): the IF-

frequency and system clock dividers and a phase detector plus charge pump are integrated to lock the

IF oscillator to the external system clock. The oscillator signal drives the divider by 2 in front of the

transmit mixer. The phase locked IF- and RF- signals are converted into the transmit band (e.g. 880 -

915 MHz for GSM) by the TX- mixer. The mixer output signal leaves the chip at MO/MOX and passes

an external interstage filter to provide suppression of unwanted products. This signal reenters the chip

at the modulator input LO/LOX.

The LO signal is divided into two orthogonal carriers at the transmit frequency. The phase between the

two carriers can be fine-adjusted to 90 ° (orthogonality) by two external resistors at OFF1/OFF2 for

maximum SSB suppression. The modulator consists of two Gilbert multipliers, where the modulating

signals I(t) and Q(t) are multiplied with the RF-carriers. The outputs of both Gilbert cells are added and

amplified by a linear output stage. The modulated transmit signal is available at E/EX and is fed into a

transmitter power amplifier.

The reproduction, transmission or use of this document is not permitted without express written authority. Offenders will be liable for damages. All

rights, including rights created by patent grant or registration of a utility model or design, are reserved.

Siemens AG

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