Transimpedance oscillator having high gain amplifier
AssigneeThe Singer Company
InventorLincoln S. Ferriss
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Abstract
A transimpedance amplifier is connected in a positive regenerative loop with a crystal resonator. The transimpedance amplifier includes a high gain amplifier with a parallel resistor and capacitor thereacross. A virtual ground is created at the node between the resonator and the amplifier input thereby eliminating circuit sensitivity to inherent capacitive changes between the resonator and true ground. Components are chosen to maintain oscillations at series resonance and achieve insensitivity to changes in the motional resistance of the resonator.
Claims13
A transimpedance oscillator comprising:
- a crystal resonator having first and second terminals and having a motional resistance (R.sub.m);
- an operational amplifier having an inverting input, a non-inverting input, and an output, the first terminal of said resonator coupled to the inverting input of said amplifier, the non-inverting input of said amplifier connected to ground to thereby establish a virtual ground at said inverting input to substantially eliminate changes in the frequency of oscillation due to capacitance variations between the inverting terminal and actual ground;
- impedance means coupling the inverting input and the output of said operational amplifier for compensating changes in R.sub.m thereby maintaining the frequency of oscillation equal to the frequency of resonator series resonance;
- and
- means coupling the output of said operational amplifier and the second resonator terminal in a positive feedback loop between the first resonator terminal and the second resonator terminal.
A transimpedance oscillator comprising:
- a crystal resonator having first and second terminals;
- a high gain operational amplifier having an inverting input, a non-inverting input and an output, the inverting input of said amplifier coupled to the first terminal of the resonator, said non-inverting input grounded for maintaining the inverting input at a virtual ground thereby substantially eliminating the effect of capacitive changes between the inverting terminal and actual ground;
- a parallel combination of a capacitor and variable resistive device coupled between the inverting input and the output of said operational amplifier for maintaining a stable frequency of oscillation equal to that of the series resonance of the crystal resonator;
- an inverting amplifier having an input resistor and a feedback resistor, said input resistor coupling the inverting amplifier to the output of said operational amplifier for restoring the original polarity of a signal present at the inverting input of said operational amplifier;
- means coupling the output terminal of said inverting amplifier to the second terminal of said resonator;
- and
- automatic gain control means having its input coupled to the output of said inverting amplifier for sensing fluctuations of voltage thereat, the output of the automatic gain control means coupled to control said variable resistive device.
Dependencies are inferred from the claim text.