Adaptive spectral noise shaping to improve time to digital converter quantization resolution using dithering
First Claim
1. A method of adaptively reducing quantization noise in a closed loop control system, said method comprising the steps of:
- providing a reference analog quantity;
providing a variable analog quantity;
applying dithered spectral noise shaping to said reference analog quantity to generate a reference noise shaped quantity;
calculating a quantized difference between said reference noise shaped quantity and said variable analog quantity; and
filtering said quantized difference to obtain a control signal of said variable analog quantity.
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Abstract
A novel and useful apparatus for and method of improving the quantization resolution of a time to digital converter in a digital PLL using noise shaping. The TDC quantization noise shaping scheme is effective to reduce the TDC quantization noise to acceptable levels especially in the case of integer-N channel operation. The mechanism monitors the output of the TDC circuit and adaptively generates a dither (i.e. delay) sequence based on the output. The dither sequence is applied to the frequency reference clock used in the TDC which adjusts the timing alignment between the edges of the frequency reference clock and the RF oscillator clock. The dynamic alignment changes effectively shape the quantization noise of the TDC. By shaping the quantization noise, a much finer in-band TDC resolution is achieved resulting in the quantization noise being pushed out to high frequencies where the PLL low pass characteristic effectively filters it out.
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Citations
43 Claims
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1. A method of adaptively reducing quantization noise in a closed loop control system, said method comprising the steps of:
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providing a reference analog quantity; providing a variable analog quantity; applying dithered spectral noise shaping to said reference analog quantity to generate a reference noise shaped quantity; calculating a quantized difference between said reference noise shaped quantity and said variable analog quantity; and filtering said quantized difference to obtain a control signal of said variable analog quantity. - View Dependent Claims (2, 3, 4, 5)
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6. A method of reducing effects of quantization noise in a time to digital converter (TDC) in a phase locked loop (PLL), comprising:
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determining a noise shaping sequence to apply to a frequency reference clock in accordance with an output of said TDC; and applying said noise shaping sequence to said frequency reference clock thereby aligning edges of said frequency reference clock with respect to the edges of an RF oscillator clock with an adaptive offset such that TDC quantization noise is reduced. - View Dependent Claims (7, 8, 9, 10)
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11. A method of shaping time to digital converter (TDC) quantization noise for use in a phase locked loop (PLL), said method comprising the steps of:
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providing a frequency reference clock signal; determining a dither to apply to said frequency reference clock signal in accordance with an output of said TDC; and dithering said frequency reference clock signal in accordance with said dither to yield high pass frequency shaped quantization noise. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18)
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19. A method of improving resolution of a time to digital converter (TDC) for use in a phase locked loop (PLL) incorporating a controllable oscillator, said method comprising the steps of:
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providing a frequency reference clock signal; estimating drift direction of said controllable oscillator; determining a phase offset of an RF output signal of said controllable oscillator with respect to said frequency reference clock signal; detecting low frequency activity in an output signal of said TDC; and applying dithering to an input of said TDC in a direction opposite to the drift direction of said controllable oscillator, thereby frequency shaping quantization noise of said TDC. - View Dependent Claims (20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. A time to digital converter (TDC) for use in a phase locked loop (PLL), comprising:
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measurement means for measuring a quantized time difference between a frequency reference clock and an RF oscillator clock; noise shaping means coupled to said measurement means, said noise shaping means comprising; means for determining a dither to apply to said frequency reference clock in accordance with said measured quantized time difference; and means for dithering said frequency reference clock in accordance with said dither resulting in high pass frequency noise shaping of said quantized time difference. - View Dependent Claims (30, 31, 32, 33, 34, 35)
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36. A radio, comprising:
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a transmitter, said transmitter comprising a phase locked loop (PLL) incorporating a time to digital converter (TDC) circuit, said TDC circuit comprising; measurement means for measuring a quantized time difference between a frequency reference clock and a radio frequency (RF) oscillator clock; noise shaping means coupled to said measurement means, said noise shaping means comprising; means for determining a dither to apply to said frequency reference clock in accordance with said measured quantized time difference; means for dithering said frequency reference clock in accordance with said sequence resulting in high pass frequency shaped TDC quantization noise; a receiver; and a baseband processor coupled to said transmitter and said receiver. - View Dependent Claims (37, 38, 39)
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40. A mobile communications device, comprising:
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a cellular radio comprising a transmitter and receiver; said transmitter comprising a phase locked loop (PLL) incorporating a time to digital converter (TDC) circuit, said TDC circuit comprising; measurement means for measuring a quantized time difference between a frequency reference clock and a radio frequency (RF) oscillator clock; noise shaping means coupled to said measurement means, said noise shaping means comprising; means for determining a dither to apply to said frequency reference clock in accordance with said measured quantized time difference; means for dithering said frequency reference clock in accordance with said dither resulting in high pass frequency shaped TDC quantization noise; a baseband processor coupled to said transmitter and receiver. - View Dependent Claims (41, 42, 43)
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Specification