Oscillator circuits and methods to compensate frequency pulling

Patent metadata

Field	Value
Publication number	US-9257996-B2
Application number	US-201514741731-A
Country	US
Kind code	B2
Filing date	Jun 17, 2015
Priority date	Jun 30, 2014
Publication date	Feb 9, 2016
Grant date	Feb 9, 2016

Abstract

An oscillator circuit may include a local oscillator to generate a carrier signal having a tunable frequency, a first modulator and a power amplifier coupled in cascade to the local oscillator to generate an output signal. The first modulator may be activated from a first modulating signal having a first frequency alternatively defining ON and OFF states of the first modulator. An estimator unit may receive the carrier signal during a time window and detect an estimated frequency variation of the carrier signal during the ON and OFF states. A compensation unit may include a second modulator to generate a compensation signal proportional to the estimated frequency variation and modulated with a second modulating frequency. The second modulating frequency may be substantially the same as the first modulating frequency, and the compensation signal may be added to a bias signal of the local oscillator to tune the tunable frequency.

First claim

That which is claimed is:

1. An oscillator circuit comprising:
a local oscillator configured to generate a carrier signal having a tunable frequency;
a first modulator and a power amplifier coupled to the local oscillator and configured to generate an output signal, the first modulator configured to be activated from a first modulating signal alternatively defining ON and OFF states of the first modulator;
an estimator unit configured to receive the carrier signal during a time window and to detect an estimated frequency variation of the carrier signal during the ON and OFF states of the first modulator; and
a compensation unit coupled to the local oscillator and comprising a second modulator configured to generate a compensation signal for tuning the tunable frequency, the compensation signal being related to the estimated frequency variation based upon a second modulating signal different than the first modulating signal.

2. The oscillator circuit of claim 1 wherein the compensation unit further comprises a logic unit coupled to said second modulator; and wherein the logic unit is configured to receive the estimated frequency variation and to define a pre-compensation signal.

3. The oscillator circuit of claim 2 wherein the logic unit is configured to generate an output digital signal; and wherein the compensation unit further comprises a digital-to-analog converter configured to receive the output digital signal from the logic unit and to generate the pre-compensation signal.

4. The oscillator circuit of claim 1 wherein the local oscillator comprises an input terminal; and further comprising a first adder coupling the input terminal of the local oscillator to a voltage source, the first adder being configured to generate a voltage compensation signal by summing a bias voltage signal generated by the voltage source and the compensation signal generated by the compensation unit.

5. The oscillator circuit of claim 4 wherein the local oscillator comprises an input bias terminal; and further comprising a second adder coupling the input bias terminal to a current source, the second adder being configured to generate a current compensation signal by summing a bias current signal generated by the current source and the compensation signal generated by the compensation unit.

6. The oscillator circuit of claim 1 wherein the compensation unit comprises a finite state machine.

7. The oscillator circuit of claim 1 wherein the first and second modulating signals have a same frequency and a different duty cycle.

8. A transceiver comprising:
a transmitter comprising
a local oscillator configured to generate a carrier signal having a tunable frequency,
a first modulator and a power amplifier coupled to the local oscillator and configured to generate an output signal, the first modulator configured to be activated from a first modulating signal alternatively defining ON and OFF states of the first modulator,
an estimator unit configured to receive the carrier signal during a time window and to detect an estimated frequency variation of the carrier signal during the ON and OFF states of the first modulator, and
a compensation unit coupled to the local oscillator and comprising a second modulator configured to generate a compensation signal for tuning the tunable frequency, the compensation signal being related to the estimated frequency variation based upon a second modulating signal different than the first modulating signal; and

a receiver comprising
a low-noise amplifier (LNA) having an input for a received signal and an output,
an adder having a first input coupled to output of the LNA, a second input coupled to the carrier signal, and an output, and
a demodulator coupled to the output of the adder for demodulating the signal output by the adder at a same frequency associated with the first modulation signal.

9. The transceiver of claim 8 wherein said transmitter transmits radar signals; wherein the first and second modulating signals have a modulating frequency of 24 GHz; and wherein the estimated frequency variation is less than 1 MHz.

10. The transceiver of claim 8 wherein the compensation unit further comprises a logic unit coupled to the second modulator; and wherein the logic unit is configured to receive the estimated frequency variation and to define a pre-compensation signal.

11. The transceiver of claim 10 wherein the logic unit is configured to generate an output digital signal; and wherein the compensation unit further comprises a digital-to-analog converter configured to receive the output digital signal from the logic unit and to generate the pre-compensation signal.

12. The transceiver of claim 8 wherein the compensation unit comprises a finite state machine.

13. The transceiver of claim 8 wherein the first and second modulating signals have a same frequency and a different duty cycle.

14. A method to compensate frequency pulling in an oscillator circuit comprising:
generating a carrier signal using a local oscillator operating at a tunable frequency;
modulating the carrier signal based upon a first modulating signal by obtaining a modulated carrier signal and amplifying the modulated carrier signal to generate an output signal;
processing the carrier signal in a time window and based upon a clock signal to define, during the time window, first time intervals and second time intervals;
estimating a first estimated frequency during the first time intervals and a second estimated frequency during the second time intervals;
determining an estimating frequency variation of the carrier signal as a difference between the first estimated frequency and the second estimated frequency;
generating a pre-compensation signal from the estimated frequency variation value;
modulating the pre-compensation signal with a second modulating signal different than the first modulating signal to obtain a compensation signal; and
tuning the local oscillator based upon the compensation signal.

15. The method of claim 14 wherein processing the carrier signal comprises:
providing the first modulating signal as the clock signal;
defining a logic state N of the local oscillator by using a previous logic state N−1 of the local oscillator; and
generating an output digital signal using the defined logic state (N) of the local oscillator;
converting the output digital signal into an analog pre-compensation signal.

16. The method of claim 14 wherein the first and second modulating signals have a same frequency and a different duty cycle.

17. The method of claim 14 wherein the oscillator is implemented in a transceiver comprising a transmitter and receiver; and further comprising:
transmitting an output signal from the transmitter and receiving an input signal at the receiver;
amplifying the input signal and combining the input signal with the carrier signal to produce a receiving signal; and
demodulating the receiving signal using a demodulator switch at a same frequency associated with the first modulation signal.

Assignees

• St Microelectronics Srl

Inventors

• Scuderi Angelo
• Calcagno Antonino
• Scaccianoce Salvatore

Classifications

• H04B7/00

  Radio transmission systems, i.e. using radiation field (H04B10/00, H04B15/00 take precedence) · CPC title

• H03L7/02 Primary

  using a frequency discriminator comprising a passive frequency-determining element · CPC title

• H04L25/4902

  Pulse width modulation; Pulse position modulation · CPC title

• H03L7/18

  using a frequency divider or counter in the loop (H03L7/20, H03L7/22 take precedence) · CPC title

• H04B1/38

  Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving · CPC title