User Guide

RH-25
System Module CCS Technical Documentation
Page 30 ©Nokia Corporation Confidential Issue 1 10/2003
As the previous figure clearly shows, most of the RF functions are centered around Taco
RF ASIC. Receiver IF stages, low-band LNA, PLLs, RXVHF oscillator, TX VHF VCO active
part and loop filter, high-band and low-band TX up-converters, TX IF stages, IQ modula-
tor and demodulator and reference oscillator buffering are all integrated on single chip.
Taco design and sample testing are carried out by ASIC team. Application responsibility
lies on RF design team as well as the components outside Taco. Externally sourced key
components are:
• 19.44 MHz VCTCXO
• 2 GHz UHF VCO
• 800MHz PA
• 1900MHz PA
• Power detector module
• 1900MHz LNA transistor
• Duplexer low band
• Duplexer high band
• RX800, RX1900, TX800, and TX1900 SAWs
• RX IF and TX IF Filters
The specifications for all key components are maintained by RF team and are available in
network.
Circuit Diagrams and PWB Layout
Receiver
Receiver design and system partition come from Snoopy AD project. The receiver shows a
superheterodyne structure with zero 2nd IF. Low-band and high- band receivers have
separate front ends from diplexer to the 1st IF. Most of the receiver functions are inte-
grated in RF ASIC. The only functions out of the chip are high-band LNA, duplexers, and
SAW filters. In spite of a bit different component selection, receiver characteristics are
very similar on both bands.
An active 1st down-converter sets naturally high gain requirements for preceding stages.
Hence, losses in very selective front end filters are minimized down to the limits set by
filter technologies used and component sizes. LNA gain is set up to 16dB, which is close
to the maximum available stable gain from a single-stage amplifier. LNAs are not exactly
noise matched in order to keep pass band gain ripple in minimum. Filters have relative
tight stop band requirements, which are not all set by the system requirements but the
interference free operation in the field. In this receiver structure, linearity lies heavily on