Frequency translator using a cordic phase rotator
First Claim
1. A frequency translator, comprising:
- a CORDIC phase rotator that rotates an input signal by a phase angle of rotation using shift and add functions;
a stochastic rounding apparatus that reduces error due to truncation of a result of higher precision arithmetic, said stochastic rounding apparatus including an adder that adds a multi-bit random number with truncated least significant bits of an output of said CORDIC phase rotator; and
a dithering apparatus that eliminates harmonics caused by digital to analog converter non-linearity, including a second adder that adds a 1-bit random number with an output of said stochastic rounding apparatus, wherein an output of said fourth adder is provided to a digital to analog converter.
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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.
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Citations
8 Claims
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1. A frequency translator, comprising:
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a CORDIC phase rotator that rotates an input signal by a phase angle of rotation using shift and add functions;
a stochastic rounding apparatus that reduces error due to truncation of a result of higher precision arithmetic, said stochastic rounding apparatus including an adder that adds a multi-bit random number with truncated least significant bits of an output of said CORDIC phase rotator; and
a dithering apparatus that eliminates harmonics caused by digital to analog converter non-linearity, including a second adder that adds a 1-bit random number with an output of said stochastic rounding apparatus, wherein an output of said fourth adder is provided to a digital to analog converter. - View Dependent Claims (2, 3)
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4. A method for translating a signal in frequency, comprising:
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rotating an input signal by a phase angle of rotation using shift and add functions of a CORDIC phase rotator;
adding a multi-bit random number with truncated least significant bits of an output of said rotation and adding a carry bit produced by said adding of said multi-bit random number to the most significant bits of said rotation to produce a first output, thereby reducing error due to truncation of a result of higher precision arithmetic; and
adding a 1-bit random number with said first output and providing a second output to a digital to analog converter, thereby eliminating harmonics caused by digital to analog converter non-linearity. - View Dependent Claims (5)
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6. A method for transmitting a signal, comprising the steps of:
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generating a digital representation of the signal to transmit;
applying successive complex-valued samples of the signal to a CORDIC phase rotator;
rotating each complex-valued sample by phase angle to achieve a desired frequency translation;
stochastically rounding the rotated complex-valued samples to reduce error due to truncation of a result of higher precision arithmetic, said stochastic rounding apparatus including an adder that adds a multi-bit random number with truncated least significant bits of an output of said CORDIC phase rotator;
adding a dither signal to the stochastically rounded samples to generate a transmission signal, wherein said dither signal is a 1-bit random number that eliminates harmonics caused by digital to analog converter non-linearity;
converting the transmission signal to an analog transmission signal; and
transmitting the analog transmission signal. - View Dependent Claims (7, 8)
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Specification