Quadrature Filter Approximation for Reconstructing the Complex Envelope of a Bandpass Signal Sampled Directly With a Two-Channel TIADC

A general and flexible technique is proposed for sampling the complex envelope of a bandpass signal by using a nonuniformly interleaved two-channel analog-to-digital converter (TIADC). The signal is sampled directly without any demodulation operation, but the two sampling channels are not uniformly interleaved, since some TIADC timing offsets are rendered forbidden. The proposed complex envelope sampling scheme requires the implementation of two digital FIR filters and a discrete-time modulator. Quadrature sampling, a special case that assumes certain parameter relations, is investigated as an approximation technique. Computer simulations are presented and illustrate a −57dB mean-square error (MSE) can be achieved via quadrature approximation for sufficiently large filter orders.