Apparatuses and methods for sample rate conversion

An apparatus that converts a signal from one sampling domain to an alternate sampling domain, comprising:

• an input line for accepting an input signal;
• a processing branch, which includes:
• (a) a branch input coupled to the input line for inputting input data samples that are discrete in time and in value;
• (b) a quadrature downconverter, having an input coupled to the branch input, that uses sine and cosine sequences to convert the input data samples into quadrature baseband and in-phase baseband outputs;
• (c) a first lowpass filter coupled to the quadrature baseband outputs and a second lowpass filter coupled to the in-phase baseband outputs of the quadrature downconverter;
• (d) a first interpolator coupled to an output of the first lowpass filter and a second interpolator coupled to an output of the second lowpass filter, each also having an input for inputting a variable interpolant value;
• and (e) a rotation matrix multiplier having a first input for inputting the variable interpolant value and a second input for inputting complex-valued data samples,
• wherein the rotation matrix multiplier applies a phase rotation to the complex-valued data samples at its second input,
• wherein at least one of:
• (i) the rotation matrix multiplier is included within the quadrature downconverter or (ii) the second input of the rotation matrix multiplier is coupled to the quadrature baseband and in-phase baseband outputs of the quadrature downconverter, and
• wherein input samples and output samples of said processing branch are different discrete-time representations of an underlying signal, with an output sampling interval associated with the output samples differing from an input sampling interval associated with the input samples by an amount that depends on the variable interpolant value.