Design and development of an automated demodulator calibration station
Eng, Chun Heong
Jenn, David C.
Pace, Phillip E.
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This thesis describes the design and development of an automated demodulator calibration station. Many commercial demodulator boards have an inherent problem of DC offset due to their direct down conversion architecture. It is necessary to measure the DC offset and compensate for it when the demodulator is used in a system such as a digital phase array. The proposed automated calibration station uses a combination of COTS hardware and software, such as NI PXI-1044 (PC) and LabVIEW programs, to digitally generate I and Q signals. The LabVIEW program cycles through phase shifts over a range of 00 to 3600. These signals are converted into analog outputs using NI PXI-6704 (DAC). Subsequently, these converted analog signals are fed into the modulator, going through an upconversion modulation process with an RF output. This RF output is adjusted to meet RFIN specification of the quadrature demodulator board before feeding into the board to recover the I and Q control signals, which are sampled by the NI PXI-5112 digitizer. After the full cycling of phase shifting by the modulator is completed, I and Q offsets are computed. This station has improvements over the existing manual calibration station, such as ease of use, shorter calibration time, accuracy and versatility for future modifications and improvements.
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