Changes between Initial Version and Version 1 of HardwareUsersGuides/RadioBoard_v1.4/Usage/TxDCOffset

Timestamp:

Apr 9, 2007, 11:40:07 PM (17 years ago)

Author:

murphpo

Comment:

--

HardwareUsersGuides/RadioBoard_v1.4/Usage/TxDCOffset

@@ +1 @@
+[[TracNav(HardwareUsersGuides/RadioBoard_v1.4/TOC)]]
+
+== WARP Radio Board TX DC Offset Calibration ==
+
+The radio transceiver on the WARP Radio Board uses a direct conversion architecture. One side-effect of this is a sensitivity to DC offsets in the transmitted signal. Any DC component in the transmit waveform results in carrier leakage at RF. In addition to any DC component in the user's transmitted waveform, the radio board itself introduces a small DC offset due to variations in component values and board assembly.
+
+To avoid these problems, users should be careful to transmit waveforms with zero DC component, and should calibrate their radios.
+
+=== Calibrating a Radio ===
+
+The residual DC offset due to component variations can be estimated using a special calibration mode of the radio board. During calibration, the algorithm estimates DC offsets for the I and Q channels on a given radio board. These values are then stored to the radio board's EEPROM. Once stored, the DC calibration values can be read by user applications each time the board is used.
+
+The calibration algorithm is not publically available. However, we do distribute an FPGA configuration file which executes the calibration process automatically.
+
+ 1) Download a copy configuraiton file - TxDCO_Calibrate.bit
+ 1) Use the DIP switch on the WARP FPGA Board to select which radios should be calibrated. Each switch position corresponds to a radio. The LSB (Radio #1) is the bottom switch; MSB (Radio #4) is the top.
+ 1) Connect a serial cable to the FPGA board and set your terminal emulator to 57600bps
+ 1) Power on the FPGA board and wait for a few minutes; this allows components to warm up
+ 1) Configure the FPGA using TxDCO_Calibrate.bit
+ 1) The terminal will display the status as it runs. Wait for the calibration of each radio to complete.
+
+You can repeat this process whenever needed. In our experience, calibration values are fairly static over time but do vary with temperature.
+
+=== Using Calibration Values ===
+
+User applications should use the stored Tx DCO calibration values on power-up. The code below is an example of how this is done. This function is portable and should compile when integrated with a user application in XPS.
+
+{{{
+#!C
+
+//Assumes your hardware platform contains:
+// radio_controller_v1_08_a
+// EEPROM_v1_00_a or EEPROM_v1_01_a
+
+//Before calling this function, your application must initialize
+// the radio controller using the WarpRadio_v1_Reset() function
+
+//Your code must also include:
+// #include radio_prototypes.h
+// #include EEPROM.h
+
+void warpmac_CalibrateTxDCO () {
+        unsigned char i;
+        unsigned int thisRadio;
+        int eepromStatus = 0;
+        short calReadback = 0;
+        signed short best_I, best_Q;
+        
+        //Select which radios should be used
+        // Include RADION_ADDR to enable a radio, 0 to disable it
+        // This array must contain 4 elements corresponding to the 4 radios
+        // Use a value of RADION_ADDR (for N=[1,2,3,4]) to enable a radio
+        // Use 0 to disable a radio
+        //  For example, these arrys are valid:
+        //   {RADIO1_ADDR, RADIO2_ADDR, RADIO3_ADDR, RADIO4_ADDR} //Calibrate all four radios
+        //   {RADIO1_ADDR, 0, 0, RADIO4_ADDR} //Calibrate radios #1 and #4
+        //  But these are not:
+        //   {RADIO2_ADDR, RADIO1_ADDR, 0, 0} //Out of order
+        //   {RADIO1_ADDR} //Not enough elements
+
+        unsigned int selectedRadios[4] = {RADIO1_ADDR, RADIO2_ADDR, 0, 0};
+
+        for(i=0; i<4; i++)
+        {
+                thisRadio = selectedRadios[i];
+
+                //Only read values for enabled radios
+                if(thisRadio > 0)
+                {
+                        //Select the EEPROM on the current radio board
+                        eepromStatus = WarpEEPROM_EEPROMSelect((unsigned int*)XPAR_EEPROM_0_BASEADDR, i);
+
+                        //Initialize the EEPROM controller
+                        eepromStatus = WarpEEPROM_Initialize((unsigned int*)XPAR_EEPROM_0_BASEADDR);
+
+                        //Read the Tx DCO values
+                        calReadback = WarpEEPROM_ReadRadioCal((unsigned int*)XPAR_EEPROM_0_BASEADDR, 2, 0);
+        
+                        //Scale the stored values
+                        best_I = (signed short)(((signed char)(calReadback & 0xFF))<<1);
+                        best_Q = (signed short)(((signed char)((calReadback>>8) & 0xFF))<<1);
+        
+                        //Optional debug output; useful to check whether the values are valid
+                        xil_printf("\r\nRadio #%d TxDCO - I: %d Q: %d\r\n", i, best_I, best_Q);
+        
+                        //Finally, write the Tx DCO values to the DAC
+                        WarpRadio_v1_DACOffsetAdj(ICHAN, best_I, thisRadio);
+                        WarpRadio_v1_DACOffsetAdj(QCHAN, best_Q, thisRadio);
+                }
+        }
+
+        return;
+}
+}}}