Programmable VCO, method of calibrating the VCO, PLL circuit with programmable VCO, and setup method for the PLL circuit
The PLL circuit comprises a phase/frequency detector ( 302 ), a loop filter ( 304, 306 ), a VCO ( 308 ) and a feedback loop ( 320 ). The VCO can be electrically disconnected from the PLL and comprises a programmable trimming circuit ( 316 ) and a current-controlled oscillator ( 318 ). For calibration the VCO is electrically disconnected from the loop filter and from the feedback loop, a constant reference voltage is applied to the voltage input (IN), a center frequency programming code (L) is applied to the trimming circuit, the center frequency programming code is iteratively adjusted until a desired center frequency is obtained, a gain programming code (K) is applied to the trimming circuit while the adjusted code is still applied, and the gain programming code is iteratively adjusted until a desired gain is obtained. Then the VCO is connected to the PLL, which is then ready for normal operation.
1. A programmable voltage-controlled oscillator, comprising:
a voltage input;
an output;
a circuit configured to generate an oscillator frequency depending on a voltage applied to the voltage input, the oscillator frequency being supplied at the output;
the circuit comprising a trimming circuit and a current-controlled oscillator, wherein the trimming circuit is configured to:
provide an input current for the current-controlled oscillator, and
provide a reference voltage; and
a feedback loop configured to apply the reference voltage to the voltage input selectively;
the trimming circuit being programmable; and
the trimming circuit being configured to derive the input current from a first programming code and a second programming code, which is independent of the first programming code.
2. The programmable voltage-controlled oscillator of claim 1 , further comprising:
a first programmable component of the trimming circuit, the first programmable component being configured to generate a first current according to the first programming code while the reference voltage is applied to the voltage input;
a second programmable component of the trimming circuit, the second programmable component being configured to generate a second current according to the second programming code while the reference voltage is applied to the voltage input; and
the input current comprising the first current and the second current.
3. The programmable voltage-controlled oscillator of claim 2 , wherein
the first programmable component comprises a digital-to-analog converter; and
the second programmable component comprises a voltage-to-current converter.
4. The programmable voltage-controlled oscillator of claim 2 , further comprising:
a current summing circuit of the trimming circuit, the current summing circuit being configured to generate the input current for the current-controlled oscillator by adding the first current and the second current.
5. The programmable voltage-controlled oscillator of claim 1 , wherein
the first programming code is variable and enables an adjustment of a center frequency; and
the second programming code is variable independently of the first programming code and enables an adjustment of a gain while the adjustment of the center frequency is maintained.
6. The programmable voltage-controlled oscillator of claim 1 , further comprising:
a first programming component configured to provide the first programming code; and
a second programming component configured to provide the second programming code.
7. A method of calibrating the programmable voltage-controlled oscillator of claim 1 , the method comprising:
generating a reference voltage using the trimming circuit;
applying the reference voltage to the voltage input using the feedback loop;
applying the first programming code;
iteratively adjusting the first programming code until a desired center frequency is obtained;
applying the second programming code while maintaining the adjusted first programming code applied; and
iteratively adjusting the second programming code until a desired gain is obtained.
8. A phase-locked loop circuit, comprising:
a phase/frequency detector;
a loop filter connected to the phase/frequency detector;
a voltage-controlled oscillator with a voltage input and an output, the voltage input being connected to the loop filter;
a first feedback loop from the output to the phase/frequency detector;
the voltage-controlled oscillator being enabled to be electrically disconnected from the loop filter and from the first feedback loop;
the voltage-controlled oscillator comprising a trimming circuit and a current-controlled oscillator, wherein the trimming circuit is configured to:
provide an input current for the current-controlled oscillator, and
provide a reference voltage; and
a second feedback loop configured to apply the reference voltage to the voltage input selectively;
the trimming circuit being programmable; and
the trimming circuit being configured to derive the input current from a first programming code and a second programming code, which is independent of the first programming code.
9. The phase-locked loop circuit of claim 8 , further comprising:
a first programmable component of the trimming circuit, the first programmable component being configured to generate a first current according to the first programming code while the reference voltage is applied to the voltage input;
a second programmable component of the trimming circuit, the second programmable component being configured to generate a second current according to the second programming code while the reference voltage is applied to the voltage input; and
the input current comprising the first current and the second current.
10. The phase-locked loop circuit of claim 9 , wherein
the first programmable component comprises a digital-to-analog converter; and
the second programmable component comprises a voltage-to-current converter.
11. The phase-locked loop circuit of claim 9 , further comprising:
a current summing circuit of the trimming circuit, the current summing circuit being configured to generate the input current for the current-controlled oscillator by adding the first current and the second current.
12. The phase-locked loop circuit of claim 8 , wherein
the first programming code is variable and enables an adjustment of a center frequency; and
the second programming code is variable independently of the first programming code and enables an adjustment of thus a gain while the adjustment of the center frequency is maintained.
13. The phase-locked loop circuit of claim 8 , further comprising:
a first programming component configured to provide the first programming code; and
a second programming component configured to provide the second programming code.
14. The phase-locked loop circuit of claim 8 , further comprising:
switches configured to allow a temporary disconnection of the voltage-controlled oscillator from the loop filter and from the feedback loop, a temporary application of the reference voltage to the voltage input of the voltage-controlled oscillator, and an alternative connection of the first programming code and the second programming code to the trimming circuit.
15. A setup method for a phase-locked loop circuit comprising a phase/frequency detector, a loop filter connected to the phase/frequency detector, a voltage-controlled oscillator with a voltage input and an output, the voltage input being connected to the loop filter, and a first feedback loop from the output to the phase/frequency detector, comprising:
disconnecting the voltage-controlled oscillator from the loop filter and from the feedback loop;
generating a reference voltage using a trimming circuit of the voltage-controlled oscillator;
applying the reference voltage to the voltage input using a second feedback loop;
applying a first programming code;
iteratively adjusting the first programming code until a desired center frequency is obtained;
applying a second programming code while maintaining the adjusted first programming code applied;
iteratively adjusting the second programming code until a desired gain is obtained; and
connecting the voltage-controlled oscillator to the loop filter and to the feedback loop, so that the phase-locked loop circuit is ready for normal operation.
16. A phase-locked loop circuit, comprising:
a phase/frequency detector;
a loop filter connected to the phase/frequency detector;
a voltage-controlled oscillator with a voltage input and an output, the voltage input being connected to the loop filter;
a first feedback loop from the output to the phase/frequency detector;
the voltage-controlled oscillator comprising a trimming circuit and a current-controlled oscillator, wherein the trimming circuit is configured to:
provide an input current for the current-controlled oscillator, and
provide a reference voltage; and
a second feedback loop configured to apply the reference voltage to the voltage input selectively;
the trimming circuit being programmable and configured to derive the input current from a first programming code and a second programming code, which is independent of the first programming code; and
switches configured to allow a temporary disconnection of the voltage-controlled oscillator from the loop filter and from the first feedback loop, a temporary application of the reference voltage to the voltage input of the voltage-controlled oscillator, and an alternative connection of the first programming code and the second programming code to the trimming circuit.