Iq Calibration Program Description - Agilent Technologies E8285A Manual

Periodic Adjustments/Calibration

IQ Calibration Program Description

IQ Calibration Program Description
The goal of IQ Calibration (see Figure 5-6 on page 138) is to minimize the carrier
feedthrough while maximizing the Rho of the IQ signal. There are four DACs
involved in this adjustment:
• buffModN_I_DC_offset_DAC,
• buffModN_Q_DC_offset DAC,
• buffModN_signal_delta_DAC,
• genRef_IQ_quad_DAC
The I and Q dc offset DACs and the signal delta DAC are on the Data Buffer
assembly and the Quad DAC is on the CDMA Generator Reference. These DACs
can be accessed in the list of Latches on the SERVICE screen. All the DACs are
initially set to 127 before starting the calibration adjustment, and the calibration is
carried out at several equally spaced frequencies between 800 and 1000 MHz.
The instrument is set into a CDMA loopback mode and the calibration is carried
out by first adjusting the I and Q dc offset DACs while monitoring the carrier
feedthrough (CFT). Both CFT and rho are measured by the Receive DSP. Once the
CFT is minimized (through an iterative process), the signal delta and the quad
DACs are adjusted while monitoring rho. When rho is maximized (again through
an iterative process), the calibration adjustment is complete. At power down, each
DAC setting at each frequency is downloaded to the calibration ROM on the
Controller assembly.
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