User Guide

CCS Technical Documentation System Module
RH-25
Issue 1 10/2003 ©Nokia Corporation Confidential Page 31
mixer design. The 2nd order distortion requirements of the mixer are set by the 'half IF'
suppression. A fully balanced mixer topology is required. Additionally, the receiver 3rd
order IIP tends to depend on active mixer IIP3 linearity due to pretty high LNA gain.
IF stages include a narrowband SAW filter on the 1st IF and an integrated lowpass filter-
ing is on zero IF. SAW filter guarantees 14dBc attenuation at alternating channels, which
gives acceptable receiver IMD performance with only moderate VHF local phase noise
performance. The local signal's partition to receiver selectivity and IMD depends then
mainly on the spectral purity of the 1st local. Zero 2nd IF stages include most of receiv-
ers signal gain, AGC control range and channel filtering.
Receiver requirements and characteristics are presented in detail in RX specification.
Frequency Synthesizers
RH-25 synthesizer consists of three synthesizers: one UHF synthesizer and two VHF syn-
thesizers. UHF synthesizer is based on integrated PLL and external UHF VCO, loop filter,
and VCTCXO. It main goal is to achieve the channel selection, thus for dual band opera-
tions associated with dual mode. Due to the RX and TX architecture, this UHF synthesizer
is used for down conversion of the received signal and for final up-conversion in trans-
mitter. A common 2GHz UHFVCO module is used for operation on both low and high
band. Frequency divider by two is integrated in Taco.
Two VHF synthesizers consist of: RX VHF Synthesizer includes integrated PLL and VCO
and loop filter and resonator. The output of RX-VHF PLL is used as LO signal for the sec-
ond mixer in receiver. TX VHF Synthesizer and Loop filter is integrated into the Taco. See
depicted block diagrams and synthesizer characteristics from Synthesizer specification
document.
Transmitter
The transmitter RF architecture is up-conversion type (desired RF spectrum is low side
injection) with (RF-) modulation and gain control at IF. The IF frequency is 180.54MHz.
The cellular band is 824.01-848.97MHz and PCS band is 1850.01-1909.95MHz.
Common IF
The RF modulator is integrated with Programmable Gain Amplifier (PGA) and IF output
buffer inside Taco RFIC-chip. I- and Q-signals, that are output signals from BB-side SW
IQ-modulator, have some filtering inside Taco before RF modulation is performed. The
required LO-signal from TXVCO is buffered with phase shifting in Taco. After modulation
(p/4 DQPSK or FM), the modulated IF signal is amplified in PGA.
Cellular Band
At operation in cellular band, the IF signal is buffered at IF output stage that is enabled
by TXP1 TX control. The maximum linear (balanced) IF signal level to 50W load is about -
8 dBm.
For proper AMPS-mode receiver (duplex) sensitivity, IF signal is filtered in strip-filter
before up-conversion. The upconverter mixer is actually a mixer with LO and output
driver being able to deliver about +6dBm linear output power. Mixer is inside Taco RF IC.