Abstract: A DC offset cancellation device is provided, including a baseband circuit, a common mode feedback (CMFB) circuit, a low-pass filter (LPF), and an amplifier. The CMFB circuit is used to set a specific common mode DC voltage in a differential circuit; thus, the CMFB circuit can be used for detecting the common mode voltage of a differential circuit, and force the voltage to a specific value by using a feedback control. Because the size of a typical CMFB circuit is much smaller than the size of an LPF, the final size of the one-LPF device is smaller than the conventional design using two LPFs.

Abstract: A method of auto-I/Q calibration in modulator and demodulator, including DC cancellation, gain imbalance and phase error calibration is provided for implementation in a front-end circuit without the use of baseband processing signal. In modulator auto-I/Q calibration, the gain amplifier, peak detector, DC gain cell and comparator and auto-I/Q calibration control logic form a calibration loop between modulator output and input buffer. The DC test vectors for their corresponding calibrations are applied to modulator to determine I/Q mismatch. In the calibration loop, the peak detector convert the carrier leakage, differential signal power level caused by the I/Q path gain mismatch and by the local quadrature mismatch into DC signal power level. The comparator is used to measure the DC different on peak deter output under different input test vector.

Abstract: A DC offset cancellation device is provided, including a baseband circuit, a common mode feedback (CMFB) circuit, a low-pass filter (LPF), and an amplifier. The CMFB circuit is used to set a specific common mode DC voltage in a differential circuit; thus, the CMFB circuit can be used for detecting the common mode voltage of a differential circuit, and force the voltage to a specific value by using a feedback control. Because the size of a typical CMFB circuit is much smaller than the size of an LPF, the final size of the one-LPF device is smaller than the conventional design using two LPFs.

Abstract: A mixer with integrated filter for single-ended image rejection is provided, including a single-end to differential (S-to-D) converter, an image rejection notch filer and four Gilbert cell switches. The mixer uses the S-to-D converter as the input cell of the mixer to replace a conventional differential pair circuit. With the converter, the mixer is directly connected to the single-ended LNA, and the output voltage swing of the LNA will be transferred into a differential signal. The image rejection filter is placed between the S-to-D converter and the Gilbert cell switches to filter the image signal from the converter. Thus, only the desired RF signal passing through the Gilbert cell switches will be converted to IF. The notch filter in the mixer of the present invention includes a third-order LC filter and a Q-enhanced circuit. The third-order LC filter has a switch capacitor array to tune both the desired frequency and the image frequency simultaneously.