= Typical Ti Calypso baseband modem design =

This is the standard Ti Calypso-based modem design used in many phones, including the Compal-built Motorola C1xx phones and
also the Openmoko GTA01 (Neo1973) and GTA02 (FreeRunner) and possibly a number of other older FIC GSM products.

It is a typically a dual- or tri-band GSM modem design with or without support for GPRS.

Block Schematic
The block layout of this modem looks like this:
Image(calypso-block.png) * Yellow: Clocks * Red: Digital Serial interfaces like SPI * Green: Analog I/Q differential baseband data * Magenta: RF signals * Blue: TSP, the time sequence port, sometimes parallel, sometimes serial Circuit Description
This is only a simplified version, ignoring the time constraints, sequencing of power-on/off events, AFC, AGC and APC.

=== GSM Rx Path === * the GSM signal from a BTS is picked up by the antenna * it reaches the Antenna Switch Module (ASM), typically a diode or MEMS switch * the Antenna Switch is configured to connect the antenna to one of the GSM/DCS/PCS Rx paths * the RF signal goes through Rx SAW filters to remove any out-of-band frequencies * the RF signal reaches the TRF6151/[wiki:Rita] zero-IF GSM Transceiver, where it is * amplified and further filtered * mixed with the frequency of the TRF6151-builtin VCO * exported as analog I/Q signals * The analog I/Q is input into the TWL3025/[wiki:Iota] ABB, where it is * sampled by an ADC * sent as serial stream of I+Q samples to the DBB via the BSP * In the DBB, the signal is * received on the RIF (Radio Inter Face) and DMA'ed into DSP API RAM * processed by the [wiki:Hardware/CalypsoDSP] DSP core inside the Calypso DBB * converted into results (e.g. a MAC block) that is sent to the ARM via API RAM * The ARM in the Calypso DBB then runs the GSM protocol stack

=== GSM Tx Path === * The ARM inside the Calypso DBB * generates some data (e.g. a MAC block) to be transmitted * writes this data plus associated commands in the API RAM * The DSP inside the Calypso DBB * executes this command during the next TDMA frame interrupt * performs forward error correction, interleaving, encryption (optional) * sends the GSM burst bits via the BSP to the ABB * The TWL3025/[wiki:Iota] ABB * receives burst bits via BSP and stores them in the burst buffer * runs those burst bits through a hardware GSMK modulator when triggered by BULENA on the TSP * outputs an Analog I/Q baseband GMSK signal to the TRF6151 * The TRF6151/[wiki:Rita] Transceiver * mixes the analog I/Q baseband signal with the VCO frequency * sends the resulting GSM-band frequency to the RF3166 * The RF3166 RF Power Amplififer * amplifies the signal according to the analog level of the APC * forwards the amplified signal to the Antenna Switch * The ASM4532 antenna switch * connects the PA output with the antenna for the duration of the burst

Glossary * ABB: Analog Base Band * AFC: Automatic Frequency Correction (tuning of the VTXCO by ABB) * APC: Automatic Power Correction (Tx Power envelope from ABB to PA) * BSP: Baseband Serial Port, like SPI * DBB: Digital Base Band, like SPI * USP: uController Serial Port * VCO: Voltage Controlled Oscillator * RFCLK: A 26MHz master clock generated by the Transceiver * CLK13M: 13MHz system clock provided by DBB * CLK32K: A 32.768kHz RTC clock signal Actual implementation in Motorola C123

[[Image(MotorolaC123:c123_pcb.jpg, 50%)]]