Patent ID: RE43236

Claim:
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, 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.