Crystal oscillator circuit with feedback control

Oscillating circuit comprising:

• a first stage amplifier having an input terminal and an output terminal;
• a second stage amplifier having an input terminal connected to said output terminal of said first stage amplifier and an output terminal;
• a feedback circuit connected between the output terminal of said second stage amplifier and the input terminal of said first stage amplifier and including a series circuit of a capacitor and a resistor;
• a crystal resonator having a resonance frequency determined by a mechanical property of a crystal and connected to said first stage amplifier;
• and
• means for determining the total gain of the circuit such that the oscillating condition is satisfied at a frequency near said resonance frequency of said crystal resonator, said total gain determining means including a gain control circuit having a detector for detecting an output signal at the output terminal of said second stage amplifier and a comparator for comparing the output of said detector and a reference signal and correspondingly controlling the gain of said second stage amplifier.