Method and apparatus of a crystal oscillator with a noiseless and amplitude based start up control loop

An apparatus comprising:

• a crystal oscillator powered through a controlled switch array;
• an output of said crystal oscillator coupled by a transmission gate to a first amplitude detector;
• a first input of a comparator coupled to an output of said first amplitude detector;
• an output of said comparator coupled to a successive approximation register (SAR);
• and
• a plurality of digital outputs of said SAR coupled to said controlled switch array.

A method of minimizing l/f noise in a crystal oscillator comprising the steps of:

• powering said crystal oscillator through a controlled switch array;
• forming said controlled switch array with a first resistor in parallel with at least one combination of another resistor in series with a transistor;
• coupling an output of said crystal oscillator to a first amplitude detector;
• coupling a first input of a control logic to an output of said first amplitude detector;
• detecting when said first input of said control logic is greater than a reference voltage;
• coupling at least one output of said control logic to said controlled switch array;
• adjusting network of said controlled switch array;
• supplying a reduced current to said crystal oscillator with said adjusted network, thereby minimizing said l/f noise in said crystal oscillator;
• coupling an output of a resistor string to an input of a second amplitude detector;
• and
• generating said reference voltage at an output of said second amplitude detector.