Voltage-controlled oscillator circuit with analogue and digital actuation
View Patent ↗A VCO circuit ( 20 ) has a coil ( 21 ) and, in parallel therewith, a constant capacitance ( 24 ) and adjustable capacitance elements ( 22, 23 ). A first capacitance element ( 22 ) is formed by one or more varactors whose capacitance can be adjusted by an analogue adjusting voltage (V tune ), while a second capacitance element ( 23 ) is formed by an arrangement comprising a plurality of capacitors which can be actuated by a digital bit word VCWD[N:1]. Digital calibration for the VCO ( 20 ) is performed by determining whether the present adjusting voltage is within a particular voltage range and, if this is not the case, the digital bit word being incremented or decremented by a bit value.
1. A voltage-controlled oscillator circuit, comprising:
at least one inductive element,
at least one first capacitive element which has a voltage-dependent capacitance and which can be actuated by an analogue adjusting voltage, and
an arrangement of second capacitive elements which is able to be configured by means of actuation using a digital bit word,
a control device for determining whether a present analogue adjusting voltage is within a prescribed voltage range and, depending on the determination, leaves the digital bit word at the present value or raises or lowers it by a bit value, wherein
the control device comprises a comparator which is supplied with the present adjusting voltage at a first input and with the upper or lower limit value of the prescribed voltage range at a second input in a way that the second input is switchably connected for receiving either the upper limit value or the lower limit value of the prescribed voltage range.
2. A voltage-controlled oscillator circuit according to claim 1 , comprising a plurality of first capacitive elements with a voltage-dependent capacitance.
3. A voltage-controlled oscillator circuit according to claim 1 , wherein
the first capacitive element is provided by a varactor.
4. A voltage-controlled oscillator circuit according to claim 1 , further comprising
a control device which stipulates whether the present analogue adjusting voltage is within a prescribed voltage range and, depending on the result, leaves the digital bit word at the present value or raises or lowers it by a bit value.
5. A voltage-controlled oscillator circuit according to claim 4 , wherein
the control device contains a comparator which is supplied with the present adjusting voltage at a first input and with the upper or lower limit value of the prescribed voltage range at a second input.
6. A Phase-locked loop comprising a voltage-controlled oscillator circuit according to claim 1 .
7. A voltage-controlled oscillator circuit, comprising:
an inductive element,
a first capacitive element having a voltage-dependent capacitance and being controlled by an analogue adjusting voltage, and
an arrangement of second capacitive elements operable to be switched by a digital bit word in such a way as to form a capacitor with variable capacitance.
8. A voltage-controlled oscillator circuit according to claim 7 , comprising a plurality of first capacitive elements with a voltage-dependent capacitance.
9. A voltage-controlled oscillator circuit according to claim 7 , wherein the first capacitive element is a varactor.
10. A Phase-locked loop comprising a voltage-controlled oscillator circuit according to claim 7 .
11. A method of operating a voltage-controlled oscillator circuit, comprising an inductive element, a first capacitive element having a voltage-dependent capacitance, and an arrangement of second capacitive elements, the method comprising the steps of:
adjusting the capacitance of the first capacitive element by an analogue adjusting voltage; and
switching a plurality of second capacitive elements on and off according to a digital bit word in such a way as to form a capacitor with variable capacitance,
determining whether the present analogue adjusting voltage is within a prescribed voltage range by supplying a comparator with a present adjusting voltage at a first input and with the upper or lower limit value of the prescribed voltage range at a second input in a way that the second input is switchably connected for receiving either the upper limit value or the lower limit value of the prescribed voltage range;
depending on the determination, leaving the digital bit word at the present value or raising or lowering it by a bit value.
12. A method according to claim 11 , wherein a plurality of first capacitive elements with a voltage-dependent capacitance is provided.
13. A method according to claim 11 , wherein the first capacitive element is a varactor.
14. A method according to claim 11 , comprising the step of using the method within a Phase-locked loop.
15. A method according to claim 14 , comprising the steps of:
setting a locking or adjusting time for the PLL;
adjusting a reference voltage to a lower or an upper reference voltage value;
selecting a desired mid-frequency and a relevant group number;
calibrating the PLL by adjusting the second capacitive elements.