Frequency translator using a cordic phase rotator
AssigneeSkyBitz, Inc.
InventorMark C. Sullivan
Life of this patent
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Abstract
A frequency translator uses a CORDIC phase rotator coupled to a phase accumulator to translate an input signal in frequency. The CORDIC phase rotator performs required phase angle rotations of input vectors using only shift and add operations. Thus, the frequency translator can be readily implemented in hardware. Higher precision arithmetic is used in the CORDIC phase rotator operations than the input vectors contain. To avoid truncation error at the output of the CORDIC phase rotator, stochastic rounding is employed. A dither signal is added to avoid errors due to nonlinear operation of D/A converters, where D/A conversion of the frequency translated signal is required.
Claims18
A frequency translator, comprising:
- a phase accumulator;
- and
- a CORDIC phase rotator coupled to the phase accumulator comprising N stages, each stage having an inphase (I) input, a quadrature (Q) input and a phase angle (θ) input, each stage further comprising a first adder to compute a quantity I±2−k Q, a second adder to compute a quantity Q±2−k I and a third adder to compute θ±φk, where each stage outputs the sum generated by each adder to be used as inputs to a succeeding stage, and wherein the Nth stage outputs an inphase component and a quadrature component from its first and second adders respectively that correspond to an input vector rotated by a desired phase angle.
A modem, comprising:
- a transmit side for transmitting a signal, the transmit side comprising:
- a digital-to-analog converter;
- and
- a frequency translator to translate the signal to a frequency suitable for transmission, wherein the frequency translator comprises:
- a CORDIC phase rotator;
- means for stochastic rounding of values output by the CORDIC phase rotator where the CORIDC phase rotator uses higher precision arithmetic than subsequent portions of the frequency translator;
- and
- means for adding a dither signal to a rounded output of the stochastic rounding means prior to inputting the rounded output to the digital-to-analog converter;
- and
- a receive side for receiving a signal, the receive side comprising:
- an analog-to-digital converter;
- and
- a frequency translator to translate the signal from a transmission frequency to a frequency suitable for processing, wherein the frequency translator comprises:
- a CORDIC phase rotator;
- and
- means for stochastic rounding of values output by the CORDIC phase rotator where the CORIDC phase rotator uses higher precision arithmetic than subsequent portions of the frequency translator.
A method for translating a signal in frequency, comprising the steps of:
- initializing a phase accumulator with an initial phase angle;
- applying an output of the phase accumulator an N-stage CORDIC phase rotator;
- calculating a quantity I±2−k Q in each stage of the N-stage CORIDC phase rotator;
- calculating a quantity Q±2−k I in each stage of the N-stage CORDIC phase rotator;
- calculating a quantity θ±φk in each stage of the N-stage CORDIC phase rotator,
- inputting to each successive stage of the N-stage CORIDC processor after the first stage an inphase (I) component, a quadrature (Q) component and phase angle θ, each of which is output by the preceding stage;
- inputting to a first stage of the N-stage CORDIC processor an inphase component and a quadrature component of a complex-valued sample of the signal to be translated in frequency, and a phase angle by which to rotate the complex-valued sample of the signal;
- outputting from a last stage of the N-stage CORDIC processor an inphase component and a quadrature component of the complex-valued sample of the signal to be translated in frequency rotated by approximately the angle stored in the phase accumulator;
- and
- adjusting the phase accumulator by an incremental phase value to achieve a frequency translation of the signal to be translated in frequency.
A method for transmitting a signal, comprising the steps of:
- generating a digital representation of the signal to transmit;
- applying successive complex-valued samples of the signal to a CORIDC phase rotator;
- rotating each complex-valued sample by phase angle to achieve a desired frequency translation;
- stochastically rounding the rotated complex-valued samples;
- adding a dither signal to the stochastically rounded samples to generate a transmission signal;
- converting the transmission signal to an analog transmission signal;
- and
- transmitting the analog transmission signal.
A method for receiving a signal, comprising the steps of:
- receiving the signal;
- converting the signal to a digital representation;
- applying successive complex-valued samples of the digital representation to a CORIDC phase rotator;
- rotating each complex-valued sample by phase angle to achieve a desired frequency translation;
- and
- stochastically rounding the rotated complex-valued samples.
Dependencies are inferred from the claim text.