TypicalCalypsoModemDesign » History » Revision 10
Revision 9 (zecke, 02/21/2016 09:59 AM) → Revision 10/12 (zecke, 02/21/2016 09:59 AM)
h1. 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. h2. Block Schematic The block layout of this modem looks like this: {{thumbnail(calypso-block.png, size=200)}} {{thumbnail(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 h2. Circuit Description This is only a simplified version, ignoring the time constraints, sequencing of power-on/off events, AFC, AGC and APC. h3. 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/[[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/[[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 [[HardwareCalypsoDSP]] 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 h3. 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/[[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/[[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 h2. 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 h2. Actual implementation in Motorola C123 {{thumbnail(MotorolaC123:c123_pcb.jpg, size=200)}} 50%)}}
