Quadrature voltage controlled oscillators with phase shift detector

• US 20050275469A1
• Filed: 06/10/2004
• Published: 12/15/2005
• Est. Priority Date: 06/10/2004
• Status: Active Grant

• Current Assignee: Theta IP, LLC
• Original Assignee: Theta Microelectronics, Inc.
• Inventors: Metaxakis, Emmanuel
• Granted Patent: US 7,075,377 B2
• Time in Patent Office: Days
• US Class Current: 331/16
• CPC Class Codes: H03B 2201/025 the means being an electronic switch for switching in or out oscillator elements
• CPC Class Codes: H03B 27/00 Generation of oscillations providing a plurality of outputs of the same frequency but differing in phase, other than merely two anti-phase outputs
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1231 the amplifier comprising one or more bipolar transistors
• CPC Class Codes: H03B 5/124 the means comprising a voltage dependent capacitance
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation

Abstract

In wireless application there is made use of a quadrature oscillators that generate signals that are capable of oscillating at quadrature of each other. The quadrature oscillator is comprised of two differential modified Colpitts oscillators. A capacitor bank allows for the selection of a desired frequency from a plurality of discrete possible frequencies. The quadrature oscillator is further coupled with a phase-error detector connected at the point-of-use of the generated ‘I’ and ‘Q’ channels and through the control of current sources provides corrections means to ensure that the phase shift at the point-of-use remains at the desired ninety degrees.

Claims

1. A quadrature oscillator circuit for generating inphase and quadrature signals comprising:

a first differential oscillator having a differential input and a differential output;

a second differential oscillator having a differential input and a differential output the first and second differential oscillators being alike;

the differential output of said first differential oscillator being connected to the differential input of said second differential oscillator;

the differential output of said second differential oscillator being connected in a cross-coupled manner to said differential input of said first differential oscillator;

whereby the differential output of said first differential oscillator will be ninety degrees from the differential output of said second differential oscillator.

2. The quadrature oscillator circuit of claim 1 wherein each said differential oscillator comprises:

a modified differential Colpitts oscillator connected in a common base mode and coupled to a capacitor bank enabling discrete selection of a resonance frequency from a plurality of frequencies;

a first differential transconducting amplifier coupled to said modified differential Colpitts oscillator for accelerating oscillation of said modified differential Colpitts oscillator;

a second differential transconducting amplifier coupled to said modified differential Colpitts oscillator for connecting the differential input of said differential oscillator to the differential output of said other differential oscillator; and

,

a current source coupled to said first differential transconducting amplifier to supply a bias current for said modified differential Colpitts oscillator.

3. The quadrature oscillator circuit of claim 2 wherein each said quadrature oscillator further comprises a common mode feedback circuit enabled to bias a common base of each of said modified differential Colpitts oscillator.

4. The quadrature oscillator circuit of claim 2 wherein fine tuning of the frequency of each of said modified Colpitts oscillators is enabled by a respective tuning capacitor.

5. The quadrature oscillator circuit of claim 4 wherein said tuning capacitor is voltage controlled.

6. The quadrature oscillator circuit of claim 1 further comprising a phase error detector (PED) connected between a point of use of differential quadrature ‘

I’ and

‘

Q’

signals to provide a feedback current to adjust phases generated by said first differential oscillator and said second differential oscillator.

7. The quadrature oscillator circuit of claim 6 wherein said PED comprises:

a first analog OR gate having an input for receiving a positive in-phase (‘

I’

) signal and a positive quadrature-phase (‘

Q’

) signal;

a second analog OR gate having an input for receiving a negative ‘

I’

signal and a negative ‘

Q’

signal;

first circuitry for summing the output from said first analog OR gate and said second analog OR gate to generate a first circuitry output;

a third analog OR gate having an input for receiving a positive ‘

I’

signal and a negative ‘

Q’

signal;

a fourth analog OR gate having a first input for receiving a negative ‘

I’

signal and a positive ‘

Q’

signal; and

, second circuitry for summing the output from said third analog OR gate and said fourth analog OR gate and there from generating a second circuitry output;

whereby the difference between said first circuitry output and said second circuitry output is a signal proportional to a phase error between the ‘

I’

signal and the ‘

Q’

signal of the quadrature signal.

8. The quadrature oscillator circuit of claim 7 wherein said PED further comprises an integrator responsive the difference between said first circuitry output and said second circuitry output.

12. The quadrature oscillator of claim 2 wherein said current source is variable to accommodate variations in loop gain with frequency of oscillation.

13. The quadrature oscillator of claim 3 wherein each common mode feedback circuit biases a respective first differential transconducting amplifier to prevent the respective first differential transconducting amplifier from going into saturation.

9-11. -11. (canceled)

14. A quadrature voltage controlled oscillator circuit for generating inphase and quadrature signals comprising:

a first differential oscillator having a differential input and a differential output;

a second differential oscillator having a differential input and a differential output, the first and second differential oscillators being alike;

the differential output of said first differential oscillator being connected to the differential input of said second differential oscillator;

the differential output of said second differential oscillator being connected in a cross-coupled manner to said differential input of said first differential oscillator;

whereby the differential output of said first differential oscillator will be ninety degrees from the differential output of said second differential oscillator;

each differential oscillator having a capacitor bank enabling a discrete selection of a resonant frequency from a plurality of frequencies;

the first differential oscillator and the second differential oscillator circuit each having a voltage controlled tuning capacitor for fine tuning of the resonant frequency.

15. The quadrature voltage controlled oscillator circuit of claim 14 wherein each said differential oscillator comprises:

a modified differential Colpitts oscillator connected in a common base mode and coupled to the capacitor bank;

a first differential transconducting amplifier coupled to said modified differential Colpitts oscillator for accelerating oscillation of said modified differential Colpitts oscillator;

a second differential transconducting amplifier coupled to said modified differential Colpitts oscillator for connecting the differential input of said differential oscillator to the differential output of said other differential oscillator; and

,

a current source coupled to said first differential transconducting amplifier to supply a bias current for said modified differential Colpitts oscillator.

16. The quadrature voltage controlled oscillator circuit of claim 15 wherein each said quadrature oscillator further comprises a common mode feedback circuit enabled to bias a common base of each of said modified differential Colpitts oscillator.

17. The quadrature voltage controlled oscillator of claim 15 wherein said current source is variable to accommodate variations in loop gain with frequency of oscillation.

18. The quadrature voltage controlled oscillator of claim 16 wherein each common mode feedback circuit biases a respective first differential transconducting amplifier to prevent the respective first differential transconducting amplifier from going into saturation.

19. The quadrature voltage controlled oscillator circuit of claim 14 further comprising a phase error detector (PED) connected between a point of use of differential quadrature ‘

I’ and

‘

Q’

signals to provide a feedback current to adjust phases generated by said first differential oscillator and said second differential oscillator.

20. The quadrature voltage controlled oscillator circuit of claim 19 wherein said PED comprises:

a first analog OR gate having an input for receiving a positive in-phase (‘

I’

) signal and a positive quadrature-phase ‘

Q’

signal;

a second analog OR gate having an input for receiving a negative ‘

I’

signal and a negative ‘

Q’

signal;

first circuitry for summing the output from said first analog OR gate and said second analog OR gate to generate a first circuitry output;

a third analog OR gate having an input for receiving a positive ‘

I’

signal and a negative ‘

Q’

signal;

a fourth analog OR gate having a first input for receiving a negative ‘

I’

signal and a positive ‘

Q’

signal; and

,

second circuitry for summing the output from said third analog OR gate and said fourth analog OR gate and there from generating a second circuitry output;

whereby the difference between said first circuitry output and said second circuitry output is a signal proportional to a phase error between the ‘

I’

signal and the ‘

Q’

signal of the quadrature signal.

21. The quadrature voltage controlled oscillator circuit of claim 20 wherein said PED further comprises an integrator responsive the difference between said first circuitry output and said second circuitry output.