Crystal controlled oscillator

• US 4,646,033 A
• Filed: 04/03/1986
• Issued: 02/24/1987
• Est. Priority Date: 04/03/1986
• Status: Expired due to Term

• Current Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Perkins, Goeffrey W.
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US06/847,414
• Time in Patent Office: 327 Days
• Field of Search: 331/116 R, 331/116 FE, 331/158, 331/159, 331/177 R, 331/117 R
• US Class Current: 331/116.00R
• CPC Class Codes: H03B 5/366 and comprising means for varying the frequency by a variable voltage or current

Abstract

A VCO including an oscillation sustaining feedback loop for maintaining the phase shift between the output and the input of a first amplifier to sustain oscillations. A diversion gate coupled with the input of the first amplifier causes the frequency of oscillation to be adjusted by introducing a phase shift within the feedback loop to thereby force the resonant frequency of a crystal connected to the input of the first amplifier to change accordingly. The feedback loop comprises a first integrator connected to the output of the first amplifier, a second amplifier having an input coupled to the output of the first amplifier and an output coupled to the input of the first amplifier and a second integrator connected to the output of the second amplifier with the output of the diversion gate being connected to the output of the second amplifier.

Claims

1. A crystal controlled oscillator, comprising:

a first amplifier having an input to which is coupled a crystal resonator and an output; and

an oscillation sustaining feedback loop coupled between said output and input of said first amplifier means for sustaining oscillations of the oscillator, said feedback loop including first integrator means coupled to said output of said first amplifier, a second amplifier having an input and an output, means coupling said input of said second amplifier to said output of said first amplifier, second integrator means coupled to said output of said second amplifier, and means for coupling said output of said second amplifier to said input of said first amplifier.

2. The oscillator of claim 1 wherein:

said first amplifier comprises a differential amplifier having first and second inputs and an output, said first input and output being said input and output of said first amplifier respectively and resistive means coupling said first input both to said feedback loop and said second input; and

said second amplifier comprises a second differential amplifier having first and second inputs and an output, said first input and said output being said input and output respectively of said second amplifier and means for coupling said second input to a bias potential.

3. The oscillator of claim 2 including means for adjusting the frequency of oscillation of the oscillator.

4. The oscillator of claim 3 wherein:

said first integrator means comprises a first capacitor connected between said output of said first amplifier and a first power supply conductor to which is supplied a ground reference potential; and

said second integrator means comprises a second capacitor connected between said output of said second amplifier and said first power supply conductor.

5. The oscillator of claim 4 wherein:

said means for coupling said input of said second amplifier to said output of said first amplifier includes a first emitter follower configured transistor; and

said means for coupling said output of said second amplifier to said input of said first amplifier includes a second emitter follower configured transistor.

6. The oscillator of claim 5 wherein said means for adjusting the frequency of oscillation includes gate means having an output coupled to said second integrator means and an input coupled to said feedback loop, said gate means being responsive to a control voltage applied thereto for causing the loop phase shift of the feedback loop to be varied accordingly to thereby force a change in the frequency of operation of said crystal resonator.

7. The oscillator of claim 6 wherein said gate means includes:

a third differential amplifier having first and second inputs and ouputs, said first and second inputs being coupled respectively to said first and second inputs of said first differential amplifier; and

steering circuit means coupled to said first and second outputs of said third differential amplifier for providing a signal at said output of said gate means having a phase that is controllable.

8. The oscillator of claim 7 wherein said steering circuit means includes:

first and second transistors the emitters of which are interconnected to said first output of said third differential amplifier; and

third and fourth transistors the emitters of which are interconnected to said second output of said third differential amplifier, the bases of said second and third transistors being interconnected, the bases of said first and fourth transistors being interconnected with said control voltage being applied across said interconnected bases of said first, second, third and fourth transistors, the collectors of said first and third transistors being interconnected to a second power supply conductor to which is supplied an operating potential and the collectors of said second and fourth transistors being interconnected to said output of said gate means.

9. The oscillator of claim 3 wherein said means for adjusting the frequency of oscillation includes gate means having an output coupled to said second integrator means and an input coupled to said feedback loop, said gate means being responsive to a control voltage applied thereto for causing the loop phase shift of the feedback loop to be varied accordingly to thereby force a change in the frequency of operation of said crystal resonator.

10. The oscillator of claim 9 wherein said gate means includes:

a third differential amplifier having first and second inputs and ouputs, said first and second inputs being coupled respectively to said first and second inputs of said first differential amplifier; and

steering circuit means coupled to said first and second outputs of said third differential amplifier for providing a signal at said output of said gate means having a phase that is controllable.

11. The oscillator of claim 10 wherein said steering circuit means includes:

first and second transistors the emitters of which are interconnected to the first output of said third differential amplifier; and

third and fourth transistors the emitters of which are interconnected to said second output of said third differential amplifier, the bases of said second and third transistors being interconnected, the bases of said first and fourth transistors being interconnected with said control voltage being applied across said interconnected bases of said first, second, third and fourth transistors, the collectors of said first and third transistors being interconnected to a power supply conductor to which is supplied an operating potential and the collectors of said second and fourth transistors being interconnected to said output of said gate means.