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TypicalCalypsoModemDesign » History » Version 10

zecke, 02/21/2016 09:59 AM

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h1. Typical Ti Calypso baseband modem design
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This is the standard Ti Calypso-based modem design used in many phones, including the Compal-built Motorola C1xx phones and
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also the Openmoko GTA01 (Neo1973) and GTA02 (FreeRunner) and possibly a number of other older FIC GSM products.
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It is a typically a dual- or tri-band GSM modem design with or without support for GPRS.
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h2. Block Schematic
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The block layout of this modem looks like this:
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{{thumbnail(calypso-block.png, size=200)}}
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* Yellow: Clocks
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* Red: Digital Serial interfaces like SPI
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* Green: Analog I/Q differential baseband data
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* Magenta: RF signals
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* Blue: TSP, the time sequence port, sometimes parallel, sometimes serial
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h2. Circuit Description
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This is only a simplified version, ignoring the time constraints, sequencing of power-on/off events, AFC, AGC and APC.
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h3. GSM Rx Path
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* the GSM signal from a BTS is picked up by the antenna
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* it reaches the Antenna Switch Module (ASM), typically a diode or MEMS switch
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** the Antenna Switch is configured to connect the antenna to one of the GSM/DCS/PCS Rx paths
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* the RF signal goes through Rx SAW filters to remove any out-of-band frequencies
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* the RF signal reaches the TRF6151/[[Rita]] zero-IF GSM Transceiver, where it is
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** amplified and further filtered
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** mixed with the frequency of the TRF6151-builtin VCO
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** exported as analog I/Q signals
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* The analog I/Q is input into the TWL3025/[[Iota]] ABB, where it is
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** sampled by an ADC
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** sent as serial stream of I+Q samples to the DBB via the BSP
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* In the DBB, the signal is
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** received on the RIF (Radio Inter Face) and DMA'ed into DSP API RAM
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** processed by the [[HardwareCalypsoDSP]] DSP core inside the Calypso DBB
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** converted into results (e.g. a MAC block) that is sent to the ARM via API RAM
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* The ARM in the Calypso DBB then runs the GSM protocol stack
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h3. GSM Tx Path
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* The ARM inside the Calypso DBB
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** generates some data (e.g. a MAC block) to be transmitted
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** writes this data plus associated commands in the API RAM
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* The DSP inside the Calypso DBB
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** executes this command during the next TDMA frame interrupt
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** performs forward error correction, interleaving, encryption (optional)
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** sends the GSM burst bits via the BSP to the ABB
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* The TWL3025/[[Iota]] ABB
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** receives burst bits via BSP and stores them in the burst buffer
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** runs those burst bits through a hardware GSMK modulator when triggered by BULENA on the TSP
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** outputs an Analog I/Q baseband GMSK signal to the TRF6151
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* The TRF6151/[[Rita]] Transceiver
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** mixes the analog I/Q baseband signal with the VCO frequency
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** sends the resulting GSM-band frequency to the RF3166
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* The RF3166 RF Power Amplififer
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** amplifies the signal according to the analog level of the APC
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** forwards the amplified signal to the Antenna Switch
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* The ASM4532 antenna switch
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** connects the PA output with the antenna for the duration of the burst
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h2. Glossary
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* ABB: Analog Base Band
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* AFC: Automatic Frequency Correction (tuning of the VTXCO by ABB)
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* APC: Automatic Power Correction (Tx Power envelope from ABB to PA)
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* BSP: Baseband Serial Port, like SPI
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* DBB: Digital Base Band, like SPI
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* USP: uController Serial Port
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* VCO: Voltage Controlled Oscillator
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* RFCLK: A 26MHz master clock generated by the Transceiver
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* CLK13M: 13MHz system clock provided by DBB
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* CLK32K: A 32.768kHz RTC clock signal
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h2. Actual implementation in Motorola C123
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{{thumbnail(MotorolaC123:c123_pcb.jpg, size=200)}}
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