Voltage control oscillation circuit and adjusting method for the same
A voltage control oscillation (VCO) circuit and an adjusting method for the same, which enables an adjustment for suppressing the dispersion of the output characteristic in spite of the manufacture-related dispersion of element characteristics, using a simple circuit configuration, are provided. A low-pass filter 15 and a high-pass filter 16 are composed of the elements that have the same structure as elements composing the VCO circuit 11 , and a prescribed correlation is established between both elements. A corrective element 14 is connected in parallel to a main element, in which an oscillation frequency control signal VT is input, in the VCO circuit 11 . Respective frequency-gain characteristic lines of the low-pass/high-pass filters 15 and 16 have gradients reverse to each other and cross at a target gain TG. When the capacitance value lowers in dispersion, the level of an output signal SL 2 becomes higher than that of an output signal SH 2 at a reference frequency fREF to form an output level difference LD 2 . In response, an adjusting signal VCNT 2 is output in correspondence to the output level difference LD 2 to lower an oscillation frequency fVCO.
1. A voltage control oscillation circuit comprising:
a low-pass filter and/or a high-pass filter, each of which is preset to have an actual gain which is intended to be identical to a preset target gain at a reference frequency in an attenuating band according to a frequency-gain characteristic in response to an input signal having the reference frequency; and
an element that has a same structure as an element that composes the low-pass filter and/or the high-pass filter and specifies an oscillation frequency;
wherein an element parameter of the element that specifies the oscillation frequency is adjusted in correspondence to a differential between the actual gain of the low-pass filter and that of the high-pass filter, or to a differential between either of respective gains of the low-pass/high-pass filters and the target gain at the reference frequency.
2. The voltage control oscillation circuit according to claim 1 , wherein
the element specifying the oscillation frequency is a variable capacitance element having a capacitance value that is adjusted variably in correspondence to the differential.
3. The voltage control oscillation circuit according to claim 2 , wherein
an oscillation frequency control signal for controlling the oscillation frequency of the voltage control oscillation circuit and
an adjusting signal for adjusting the capacitance value are input in the variable capacitance element.
4. The voltage control oscillation circuit according to claim 3 , wherein the variable capacitance element has
a main element in which the oscillation frequency control signal is input, and
a corrective element which is connected in parallel to the main elements and in which the adjusting signal is input.
5. The voltage control oscillation circuit according to claim 1 , the oscillation circuit comprising
the low-pass filter and the high-pass filter, which are preset so that respective target gains of both filters coincide.
6. The voltage control oscillation circuit according to claim 1 , wherein
respective cut-off frequencies of the low-pass filter and/or the high-pass filter are set to coincide with the reference frequency.
7. The voltage control oscillation circuit according to claim 1 , wherein the target gain is set to be equal to a gain attenuating by 50% according to the frequency-gain characteristic.
8. The voltage control oscillation circuit according to claim 3 , the oscillation circuit comprising:
a DC conversion section that smoothes an output signal from the low-pass filter and/or from the high-pass filter; and
a comparison section that outputs the adjusting signal in correspondence to a signal level difference between the output signal from the low-pass filter and the output signal from the high-pass filter, or to a signal level difference between the output signal from the low-pass filter and the target gain, or to a signal level difference between the output signal from the high-pass filter and the target gain.
9. The voltage control oscillation circuit according to claim 8 , wherein
the comparison section outputs the adjusting signal to enlarge the capacitance value of the variable capacitance element in correspondence to respective signal level differences when the level of the output signal from the low-pass filter is higher than the level of the output signal from the high-pass filter, or the level of the output signal from the low-pass filter is higher than the level of the target gain of the low-pass filter, or the level of the target gain of the high-pass filter is higher than the level of the output signal from the high-pass filter, while
the comparison section also outputs the adjusting signal to reduce the capacitance value of the variable capacitance element in correspondence to respective signal level differences when the level of the output signal from the low-pass filter is lower than the level of the output signal from the high-pass filter, or the level of the output signal from the low-pass filter is lower than the level of the target gain of the low-pass filter, or the level of the target gain of the high-pass filter is lower than the level of the output signal from the high-pass filter.
10. An adjusting method for a voltage control oscillation circuit, the adjusting method comprising:
obtaining a differential between an actual gain of a low-pass filter and that of a high-pass filter at a reference frequency, or a differential between either of respective actual gains of the low-pass or high-pass filters and a target gain at the reference frequency; and
adjusting an element parameter that has a same structure as an element that composes the low-pass filter and/or the high-pass filter and specifies an oscillation frequency in correspondence to the differential.
11. The adjusting method for the voltage control oscillation circuit according to claim 10 , wherein:
the element parameter is a capacitance value,
the capacitance value of the element parameter is enlarged relative to a signal level difference between respective output signals and the target gain or to a signal level difference between respective output signals when a level of an output signal from the low-pass filter is higher than a level of an output signal from the high-pass filter, or the level of the output signal from the low-pass filter is higher than a level of a target gain of the low-pass filter, or a level of a target gain of the high-pass filter is higher than the level of the output signal from the high-pass filter,
while the capacitance value of the element parameter is reduced relative to respective signal level differences when the level of the output signal from the low-pass filter is lower than the level of the output signal from the high-pass filter, or the level of the output signal from the low-pass filter is lower than the level of the target gain of the low-pass filter, or the level of the target gain of the high-pass filter is lower than the level of the output signal from the high-pass filter.