The receiver architecture proposed in this brief seizes the subsampling properties of continuous-time sigma-delta (61) modulators based on distributed resonators to construct a quadrature receiver. The proposed architecture is based on a low-pass 61 modulator that subsamples an intermediate frequency signal around the sampling frequency and does not require quadrature mixers. Instead, the quadrature mixing is replaced by suitably choosing the sampling instants inside the loop. Two practical circuit implementations are proposed. The first one uses separate circuitry for the and paths. The second architecture introduces an innovative way to produce the and outputs that is immune to path mismatch due to the sharing of all the analog circuitry for both paths. The proposed modulator may be feasible for the typical IF frequencies used in cellular base stations.

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Abstract-Quadrature Σ∆ ADCs require a feedback path for both the I and the Q part of the complex feedback signal. If two separated multibit feedback DACs are used, mismatch among the unit DAC elements leads to additional mismatch noise in the output spectrum as well as an unbalance between the I and Q DAC. This paper proposes a new quadrature bandpass mismatch shaping technique. In our approach the I and Q DACs are merged into one complex DAC, which leads to near-perfect I/Q balance. To select the unit DAC elements of the complex, multibit DAC, the well-known tree structured element selection logic is generalized toward a complex structure and necessary conditions for its correct operation are derived. Finally, a very efficient first-order quadrature shaper implementation is proposed and simulations show the effectiveness of the quadrature bandpass mismatch shaping technique.

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