This adjustment is similar to the FM Path Offset Calibration, but this adjustment generates a DAC value to null the voltage offset on the differential inverting amplifier on the A6 Frac-N.
During this adjustment, when FM is enabled, the A6 Frac-N and A11 Pulse/Analog Modulation Generator may generate unwanted voltage offsets. These voltage offsets tune the Frac-N VCO from the desired frequency.
The signal generator frequency is set for 525 MHz at 0 dBm. The EXT1 input is DC-coupled and left open for this calibration. FM is enabled with an FM deviation of 100 kHz. The calibration loads the FM_OFFSET_DACs with the values calculated in the FM Path Offset Calibration. The two FM multiplexers, on the A11 Pulse/Analog Modulation Generator, have their ground inputs selected. The FM_SCALE_DAC is set to 0 and an internal voltage measurement is made on the analog bus through the FM_ABUS node. The FM1_OFFSET_DAC is set for 255 and another voltage measurement is made. From these two measurements, an Offset DAC value is calculated. If the difference between the Offset DAC value and the original FM_OFFSET_DAC values are greater than 20 DAC counts, the calibration fails. Otherwise, the difference DAC value, which takes into account the FM Path Offset and the FM Inverting Amp Offset, is stored.
Connect a GPIB cable between the controller and the signal generator being calibrated.
While performing this adjustment, follow all instructions on the controller display.
If this adjustment fails, perform the following steps in order:
Check the equipment setup (see above). If the setup is incorrect, make the necessary corrections and rerun the adjustment.
If this adjustment fails with the equipment set up properly, refer to the troubleshooting section of the signal generator's service guide. If you do not have a printed copy of the service guide (Option OBW), one is available either on the CD-ROM that came with your signal generator shipment or on the Keysight Website.
If you cannot correct the problem using the troubleshooting procedures in the Service Guide, obtain service from Keysight Technologies. Refer to Contacting Keysight Technologies.