PMB-2240 Siemens, PMB-2240 Datasheet - Page 8

• Manufacturer Part Number: PMB-2240
• Description: GSM Transmitter
• Manufacturer: Siemens

The GSM transmitter PMB2240 contains a number of functions that have been realised with multiple
chips earlier:
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.
Siemens AG
The reproduction, transmission or use of this document is not permitted without express written authority. Offenders will be liable for damages. All
- Oscillator signal input balanced or unbalanced
- RF-PLL prescaler
- IF-PLL dividers and phase detection
- TX - mixer
- I/Q modulator
rights, including rights created by patent grant or registration of a utility model or design, are reserved.
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