Low power crystal oscillator with automatic amplitude control

A low power crystal oscillator circuit, comprising

• a crystal having an input terminal and an output terminal;
• a high power supply;
• a low power supply;
• a first capacitor coupled to the input terminal of the crystal;
• a second capacitor coupled to the output terminal of the crystal;
• a first current mirror transistor coupled to the high power supply;
• a first current source configured to output a current of a first value, the first current source coupled to the first current mirror transistor;
• a second current mirror transistor coupled to the high power supply and the first current mirror transistor;
• a third current mirror transistor coupled to the high power supply;
• a second current source configured to output a current of a second value less than the first value, the second current source coupled to the third current mirror transistor;
• a fourth current mirror transistor coupled to the third current mirror transistor and the second current mirror transistor;
• a fifth current mirror transistor coupled to the high power supply, the third current mirror transistor, the fourth current mirror transistor, and first current mirror transistor;
• and
• a third capacitor coupled to the input terminal of the crystal and coupled to gate terminals of the third current mirror transistor, the fourth current mirror transistor, and the fifth current mirror transistor, the gate terminals of the third current mirror transistor, the fourth current mirror transistor, and the fifth current mirror transistor are coupled to the input terminal of the crystal;
• and
• a sixth current mirror transistor coupled to the high power supply;
• a third current source outputting current of a third value that is less than the first value, the third current source coupled to the sixth current mirror transistor;
• and
• a seventh current mirror transistor coupled to the high power supply, a gate terminal coupled to a gate terminal of the sixth current mirror transistor, and a second terminal coupled to a first terminal of the fourth current mirror transistor.

A low power crystal oscillator circuit, comprising:

• a crystal;
• a high power supply;
• a low power supply;
• a first capacitor coupled between the crystal and the low power supply;
• a second capacitor coupled between the crystal and the low power supply;
• a first current mirror transistor coupled to the high power supply;
• a first current source of a first value coupled to the first current mirror transistor;
• a second current mirror transistor coupled to the high power supply and to the first current mirror transistor;
• a third current mirror transistor coupled to the high power supply and the first current mirror transistor;
• a second current source of a second value that is less than the first value, the second current source coupled to the third current mirror transistor;
• a fourth current mirror transistor coupled to the first current mirror transistor;
• a first control transistor coupled to the high power supply, the third current mirror transistor, and a second terminal;
• a third current source outputting current of a third value that is less than the first value, the third current source coupled to the first control transistor and the low power supply;
• and
• a second control transistor coupled to the second current mirror transistor, the first control transistor, an output terminal of the crystal, and the fourth current mirror transistor.