Temperature compensated crystal oscillator

A digital temperature compensated crystal oscillator system comprising:

• a temperature to voltage converting circuit for sensing an ambient temperature of a crystal unit and outputting an analog temperature voltage signal representing a sensed ambient temperature;
• a memory and operation circuit for storing a collection of temperature compensation data items, receiving a digital temperature data signal as an input signal, providing a selected data item identified by said digital temperature data signal, and producing a digital compensation data signal in accordance with said selected data item;
• and
• a data conversion circuit for producing said digital temperature data signal in accordance with said analog temperature voltage signal from said temperature to voltage converting circuit, and for producing an analog compensation voltage signal in accordance with said digital compensation data signal from said memory and operation circuit, said data conversion circuit comprising a first section for producing an analog intermediate signal, a second section for producing said digital temperature data signal by converting said analog temperature voltage signal in accordance with said analog intermediate signal and delivering said digital temperature data signal to said memory and operation circuit, and a third section for producing said analog compensation voltage signal by converting said digital compensation data signal through said first section;
• wherein said first section comprises a resistor string circuit comprising a series combination of resistors for receiving a voltage reference and providing a plurality of voltage levels, and a decode switch circuit for selecting one of the voltage levels provided by the resistor string circuit;
• said second section comprises an ADC supplementary circuit for producing a biased voltage signal by receiving said analog temperature signal and producing a comparator output signal by comparing said analog intermediate signal from said first section with said biased voltage signal, and a temperature data generating section for performing a count down operation in accordance with said comparator output signal from said ADC supplementary circuit and producing a digital intermediate signal;
• said third section comprises a DAC supplementary circuit for producing said analog compensation signal;
• and said data conversion circuit further comprises a first switch circuit for supplying said analog intermediate signal from said first section to a selected one of said ADC supplementary circuit and said DAC supplementary circuit, and a second switch circuit for controlling said decode switch circuit by sending, to said decode switch circuit, a selected one of said digital intermediate signal produced by said temperature data generating section and said digital compensation data signal produced by said memory and operation circuit.

A digital temperature compensated crystal oscillator system comprising:

• a temperature to voltage converting circuit for sensing an ambient temperature of a crystal unit and outputting an analog temperature voltage signal representing a sensed ambient temperature;
• a memory and operation circuit for storing a collection of temperature compensation data items, receiving a digital temperature data signal as an input signal, providing a selected data item identified by said digital temperature data signal, and producing a digital compensation data signal in accordance with said selected data item;
• and
• a data conversion circuit for producing said digital temperature data signal in accordance with said analog temperature voltage signal from said temperature to voltage converting circuit, and for producing an analog compensation voltage signal in accordance with said digital compensation data signal from said memory and operation circuit, said data conversion circuit comprising a first section for producing an analog intermediate signal, a second section for producing said digital temperature data signal by converting said analog temperature voltage signal in accordance with said analog intermediate signal and delivering said digital temperature data signal to said memory and operation circuit, and a third section for producing said analog compensation voltage signal by converting said digital compensation data signal through said first section;
• wherein said first section comprises a resistor string circuit comprising a series combination of resistors for receiving a voltage reference and providing a plurality of voltage levels, and a decode switch circuit for selecting one of the voltage levels provided by the resistor string circuit;
• wherein said second section comprises an ADC supplementary circuit for producing a biased voltage signal by receiving said analog temperature signal and producing a comparator output signal by comparing said analog intermediate signal from said first section with said biased voltage signal, and a temperature data generating subsection for performing a count down operation in accordance with said comparator output signal from said ADC supplementary circuit and producing a digital intermediate signal;
• wherein said third section comprises a DAC supplementary circuit for producing said analog compensation signal;
• wherein said data conversion circuit further comprises a first connecting means comprising a first switch circuit for supplying said analog intermediate signal from said first section to a selected one of said ADC supplementary circuit and said DAC supplementary circuit, and a second connecting means for supplying one of said digital intermediate signal produced by said temperature data generating subsection and said digital compensation data signal produced by said memory and operation circuit;
• and
• wherein said DAC supplementary circuit is connected to a low pass filter having a time constant which is greater than an ADC conversion time.

A temperature compensated crystal oscillator system comprising:

• a crystal unit having a first end and a second end, the second end being connected to a ground;
• a MOS transistor comprising a drain, a source and a gate, the gate being connected to said first end of said crystal unit;
• a gate voltage fixing resistor connected between the drain and gate of the MOS transistor;
• a source resistor connected between the source of the MOS transistor and the ground;
• a series circuit of a detecting capacitor and a feedback semiconductor capacitor constituting a Colpitts oscillator circuit;
• and
• a decoupling capacitor connected between the source of the MOS transistor and a node between the detecting capacitor and the feedback semiconductor capacitor.