Automatic circuit and method for temperature compensation of oscillator frequency variation over temperature for a real time clock chip
First Claim
1. An automatic temperature compensated real-time clock (RTC) chip, comprising:
- a clock portion including a crystal oscillator block comprising crystal compensation circuitry adapted to be coupled to a crystal, said crystal compensation circuitry comprising a non-linear capacitor DAC including a plurality of load capacitors, said load capacitors having respective switches which switch respective ones of said load capacitors to change a parallel resonance frequency (fp) generated by said oscillator block, wherein said capacitor DAC is arranged so that Analog Trimming (ATR) bits received cause an arrangement of said switches to provide a non-linear change in overall load capacitance to result in a linear relationship between said fp and said ATR bits;
a temperature sensor block coupled to said crystal for measuring a temperature of at least said crystal;
an A/D converter coupled to said temperature sensor for outputting a digital temperature signal representative of said temperature of said crystal, anda DSP engine for receiving said digital temperature signal, said DSP engine calculating frequency correction needed to correct for frequency inaccuracy and determining a bit sequence comprising said ATR bits to achieve said frequency correction.
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Abstract
An automatic temperature compensated real-time clock (RTC) chip includes a clock portion having a crystal oscillator block including crystal compensation circuitry adapted to be coupled to a crystal. The crystal compensation circuitry includes a non-linear capacitor DAC including a plurality of load capacitors, wherein the load capacitors have respective switches which switch respective ones of the load capacitors to change a parallel resonance frequency (fp) generated by the oscillator block. The capacitor DAC is arranged so that Analog Trimming (ATR) bits received cause an arrangement of the switches to provide a non-linear change in overall load capacitance to result in a linear relationship between fp and the ATR bits. A temperature sensor block is coupled to the crystal for measuring a temperature of at least the crystal. An A/D converter is coupled to the temperature sensor for outputting a digital temperature signal representative of the temperature of the crystal. A DSP engine receives the digital temperature signal and calculates frequency correction needed to correct for frequency inaccuracy and determines a bit sequence including the ATR bits appropriate to achieve the frequency correction.
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Citations
35 Claims
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1. An automatic temperature compensated real-time clock (RTC) chip, comprising:
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a clock portion including a crystal oscillator block comprising crystal compensation circuitry adapted to be coupled to a crystal, said crystal compensation circuitry comprising a non-linear capacitor DAC including a plurality of load capacitors, said load capacitors having respective switches which switch respective ones of said load capacitors to change a parallel resonance frequency (fp) generated by said oscillator block, wherein said capacitor DAC is arranged so that Analog Trimming (ATR) bits received cause an arrangement of said switches to provide a non-linear change in overall load capacitance to result in a linear relationship between said fp and said ATR bits; a temperature sensor block coupled to said crystal for measuring a temperature of at least said crystal; an A/D converter coupled to said temperature sensor for outputting a digital temperature signal representative of said temperature of said crystal, and a DSP engine for receiving said digital temperature signal, said DSP engine calculating frequency correction needed to correct for frequency inaccuracy and determining a bit sequence comprising said ATR bits to achieve said frequency correction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for temperature compensating a real time clock (RTC) circuit, comprising the steps of:
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providing a real-time clock (RTC) having a crystal oscillator block comprising a crystal coupled to crystal compensation circuitry, said crystal compensation circuitry comprising a non-linear Capacitor DAC having a plurality of load capacitors having respective switches which switch respective ones of said load capacitors to change a parallel resonance frequency (fp) generated by said oscillator block, wherein said capacitor DAC is arranged so that Analog Trimming (ATR) bits received cause an arrangement of said switches to provide a non-linear change in overall load capacitance resulting in a linear relationship between said fp and said ATR bits; measuring a temperature of said crystal; generating an input code comprising said ATR bits based on said temperature to correct said fp, and frequency correcting by applying said input code as said input code vectors to said Capacitor DAC to provide a frequency shift to temperature correct an oscillator frequency of said crystal oscillator. - View Dependent Claims (16, 17, 18, 19, 20)
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21. An automatic temperature compensated real-time clock (RTC) chip, comprising:
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a clock portion including a crystal oscillator block comprising crystal compensation circuitry adapted to be coupled to a crystal, said crystal compensation circuitry comprising a non-linear capacitor DAC, wherein said non-linear capacitor DAC is arranged so that Analog Trimming (ATR) bits received cause a non-linear change in overall load capacitance to result in a linear relationship between said ATR bits and a parallel resonance frequency (fp) generated by said oscillator block; a temperature sensor block coupled to said crystal for measuring a temperature of at least said crystal; an A/D converter coupled to said temperature sensor for outputting a digital temperature signal representative of said temperature of said crystal, and a DSP engine for receiving said digital temperature signal, said DSP engine calculating frequency correction needed to correct for frequency inaccuracy and determining a bit sequence comprising said ATR bits to achieve said frequency correction. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29)
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22. A method for temperature compensating a real time clock (RTC) circuit, the method comprising:
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measuring a temperature of a crystal oscillator block; generating an input code comprising Analog Trimming (ATR) bits based on said temperature to correct a parallel resonance frequency (fp) generated by said oscillator block, and applying said input code as input code vectors to a capacitor DAC to provide a frequency shift to temperature correct an oscillator frequency of said crystal oscillator, wherein said capacitor DAC is arranged so that said ATR bits received cause a non-linear change in overall load capacitance resulting in a linear relationship between said fp and said ATR bits. - View Dependent Claims (30, 31, 32, 33, 34, 35)
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Specification