Balanced feedback oscillators

• US 4,661,785 A
• Filed: 05/22/1985
• Issued: 04/28/1987
• Est. Priority Date: 05/22/1985
• Status: Expired due to Fees

• Current Assignee: S.T. Research Company, Limited
• Original Assignee: S.T. Research Corporation (Sensys Technologies, Inc.)
• Inventors: Benjaminson, Albert
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US06/736,883
• Time in Patent Office: 706 Days
• Field of Search: 331/109, 331/116 R, 331/108 D, 331/158, 331/183, 331/56, 331/117 R, 331/167, 331/168, 331/116 FE, 331/117 FE
• US Class Current: 331/109
• CPC Class Codes: H03B 2200/0004 Butler oscillator
• CPC Class Codes: H03B 2200/0008 Colpitts oscillator
• CPC Class Codes: H03B 2200/0012 Pierce oscillator
• CPC Class Codes: H03B 2200/0098 having a balanced output signal
• CPC Class Codes: H03B 5/36 active element in amplifier being semiconductor device H03B5/323, H03B5/326 , H03B5/38 take precedence

Abstract

The oscillator circuit comprises an amplifier having a pair of inputs, a positive feedback path producing a positive feedback ratio to one of the inputs, and a negative feedback path including a series resonant circuit producing a negative feedback ratio to the other of the inputs. The positive and negative feedback paths are independent such that the current in each of the paths can be adjusted independently. In this manner, a high Q multiplier effect is achieved. Also, the circuit has an output path which is separate from the input path so that a high output signal level can be achieved while maintaining a low current through the series resonant circuit.

Claims

1. An oscillator circuit comprising:

a differential amplifier having an inverting input and a non-inverting input and having a positive feedback path connected to one of said inputs, a negative feedback path connected to the other of said inputs, and an output path;

a series resonant circuit connected in said negative feedback path; and

at least one impedance element in said positive feedback path for establishing a feedback ratio sufficient to cause oscillation to occur at the resonant frequency of said series resonant circuit;

wherein the negative feedback path is separate from said output path such that the output power of said amplifier can be controlled independently of current in said negative feedback path.

2. An oscillator circuit as claimed in claim 1 wherein said series resonant circuit comprises a piezoelectric crystal.

3. An oscillator circuit as claimed in claim 2 wherein said crystal has one side connected directly to ground.

4. An oscillator circuit as claimed in claim 3 wherein said crystal has another side connected to said other input of said differential amplifier.

5. An oscillator circuit as claimed in claim 1 further including limiting circuit means for varying the feedback ratio of said positive feedback path in response to an output level of said output path.

6. An oscillator circuit, comprising:

a differential amplifier having an inverting input and a non-inverting input having;

a positive feedback path producing a positive feedback ratio to one of said inputs; and

a negative feedback path including a series resonant circuit producing a negative feedback ratio to the other of said inputs;

wherein said positive and negative feedback paths are independent such that the current in each of said paths can be adjusted independently, said paths being adjusted to produce oscillation at the resonant frequency of said resonant circuit.

7. An oscillator as claimed in claim 6 wherein said series resonant circuit is a piezoelectric crystal.

8. An oscillator circuit as claimed in claim 7 wherein said piezoelectric crystal has a pair of leads, one of said leads being connected to ground.

9. An oscillator circuit as claimed in claim 6 wherein said differential amplifier comprises two transistors having respective collectors, and a resonant circuit connected between said collectors.

10. An oscillator circuit as claimed in claim 6 wherein said positive feedback path comprises a capacitive divider connected between said output and said non-inverting input.

11. An oscillator circuit as claimed in claim 10 wherein said negative feedback path includes a divider comprising a resistance and said series resonant circuit connected between said output and said inverting input.

12. An oscillator circuit as claimed in claim 6 wherein said differential amplifier comprises a pair of transistors and an inductor connecting bases of said transistors together.

13. An oscillator circuit as claimed in claim 6 and further including an amplitude limiting control circuit for controlling the positive feedback ratio in response to the amplitude of a signal on said output.

14. An oscillator circuit as claimed in claim 13 wherein said limiting control circuit comprises a variable capacitor in said positive feedback path and means to vary the capacitance of said capacitor depending upon the output of said amplifier.

15. An oscillator circuit as claimed in claim 6 wherein said differential amplifier is an integrated circuit differential amplifier.

16. An oscillator circuit as claimed in claim 15 wherein said integrated circuit differential amplifier has a low impedance output and said positive feedback path comprises a resistive voltage divider connected between said output and said non-inverting input.

17. An oscillator circuit as claimed in claim 16 wherein said series resonant circuit comprises a piezoelectric crystal.

18. An oscillator circuit as claimed in claim 15 further including a second resonant circuit connected between said inverting and non-inverting inputs.