High frequency precision oscillators having stable temperature characteristics
View Patent ↗An oscillator circuit includes an adjustable frequency oscillator configured to free-run at a first frequency below a desired second target frequency. This adjustable frequency oscillator is configured to modulate a frequency of its periodic output signal upwards from the first frequency to the second frequency in response to a feedback bias current. A divider is also provided, which is configured to convert the periodic output signal to a reduced-frequency control signal. This reduced-frequency control signal is provided to a frequency-to-current (F2C) converter, which is configured to drive the adjustable frequency oscillator with the feedback bias current (e.g., pull-down current) in response to the reduced-frequency control signal.
1. An oscillator circuit, comprising:
an adjustable frequency oscillator configured to free-run at a first frequency below a desired second frequency, said adjustable frequency oscillator configured to modulate a frequency of its periodic output signal upwards from the first frequency to the second frequency in response to a feedback bias current;
a divider configured to convert the periodic output signal to a reduced-frequency control signal; and
a frequency-to-current converter configured to drive the adjustable frequency oscillator with the feedback bias current in response to the reduced-frequency control signal, said frequency-to-current converter comprising a cascaded arrangement of a frequency-to-voltage converter and an error amplifier, said frequency-to-voltage converter comprising a ramp generator and said error amplifier comprising a sampling amplifier.
2. The oscillator circuit of claim 1 , wherein the frequency-to-voltage converter is responsive to a bandgap reference voltage.
3. The oscillator circuit of claim 1 , wherein the frequency-to-voltage converter is configured to perform a frequency-to-voltage conversion at the frequency of the reduced-frequency control signal.
4. The oscillator circuit of claim 3 , wherein said divider is configured to perform a divide-by-2 N operation, where N is an integer greater than two.
5. The oscillator circuit of claim 1 , wherein the frequency-to-voltage converter comprises a frequency measurement decoder electrically coupled to a plurality of stages within said divider.
6. The oscillator circuit of claim 1 , further comprising a bias signal generator configured to generate a first bias voltage, which is provided to said frequency-to-current converter.
7. The oscillator circuit of claim 6 , wherein said frequency-to-current converter is configured to generate the feedback bias current at a first output thereof; and wherein said adjustable frequency oscillator and said bias signal generator are electrically coupled to the first output of said frequency-to-current converter.
8. The oscillator circuit of claim 1 , wherein said adjustable frequency oscillator is a dual-ramp oscillator.
9. An oscillator circuit, comprising:
an oscillator configured to modulate a frequency of its periodic output signal in response to a feedback bias current;
a divider configured to convert the periodic output signal to a reduced-frequency control signal; and
a frequency-to-current converter configured to drive said oscillator with the feedback bias current in response to the reduced-frequency control signal, said frequency-to-current converter comprising a cascaded arrangement of a frequency-to-voltage converter, which comprises a ramp generator, and a sampling error amplifier.
10. The oscillator circuit of claim 9 , wherein the frequency-to-voltage converter comprises a frequency measurement decoder electrically coupled to a plurality of stages within said divider.
11. The oscillator circuit of claim 9 , further comprising a bias signal generator configured to generate a first bias voltage, which is provided to said frequency-to-current converter.
12. The oscillator circuit of claim 11 , wherein said frequency-to-current converter is configured to generate the feedback bias current at a first output thereof; and wherein said adjustable frequency oscillator and said bias signal generator are electrically coupled to the first output of said frequency-to-current converter.
13. The oscillator circuit of claim 9 , wherein said oscillator is a dual-ramp oscillator.