A direct RF-to-baseband quadrature subsampling receiver using a low cost ADC

This paper presents a novel receiver using direct complex subsampling. In this approach no frequency conversion is used, but therefore bandpass sampling in combination with nonuniform sampling. A special sampling pattern for the analog to digital conversion is used. The resulting sampling frequency is below the carrier frequency, like in standard bandpass sampling receivers. Therefore the requirements for the analog-digital converter (ADC) and digital signal processor (DSP) are decreased. The sample and hold stage of the ADC still has to meet the requirements for the carrier frequency. The corresponding sampling scheme and its signal processing are described. A simulation of a QPSK receiver is presented. The proposed architecture is validated using a low cost commercial-off-the-shelf (COTS) ADC along with some testing and measurements. The receiver works for the industrial, scientific and medical band (ISM) carrier frequency at 13.56 MHz, which is commonly used for short range devices like radio-frequency identification (RFID) applications.