Integration method and integration circuit offering improved signal-to-noise ratio, and voltage-controlled oscillator and frequency-voltage converter employing integration circuit

An integration circuit, comprising:

• an integrating capacitor;
• a current source for supplying a current to said integrating capacitor;
• a switch installed on a path along which a current is supplied from said current source to said integrating capacitor;
• a detection circuit for detecting a voltage developed at said integrating capacitor;
• a control circuit for controlling said switch so that a current will be supplied from said current source to said integrating capacitor during an integration period;
• and
• a charge/discharge circuit comprising:
• a first current source for supplying a current proportional to a voltage level of an input signal to said integrating capacitor;
• and
• a second current source for causing said current proportional to the voltage level of said input signal to flow from said integrating capacitor, wherein
• said integration period falls into a current supply period and a stop period;
• and
• said control circuit controls said switch so that a current will be supplied from said current source to said integrating capacitor during said current supply period and no current will be supplied from said current source to said integrating capacitor during said stop period, and wherein
• said control circuit comprises:
• a stop switch installed on a path along which a current flows for charging or discharging said integrating capacitor;
• a first switch interposed between said first current source and stop switch;
• a second switch interposed between said second current source and stop switch and alternately closed and opened in association with phases opposite to phases with which said first switch is closed and opened;
• and
• a stop signal generation circuit for generating a stop signal, which becomes active during said predetermined period, in response to said oscillating signal, and said stop switch is opened in response to said stop signal.

A voltage controlled oscillator for outputting an oscillating signal whose frequency varies depending on the voltage level of an input signal, comprising:

• an integrating capacitor;
• a charge/discharge circuit for charging or discharging said integrating capacitor with a current proportional to the voltage level of said input signal;
• a reference level source for selectively outputting a first reference level and second reference level;
• a comparison circuit for comparing a voltage developed at said integrating capacitor with a reference level output from said reference level source, and outputting the results of comparision in the form of said oscillating signal;
• and
• a control circuit for controlling charge and discharge of said integrating capacitor by said charge/discharge circuit, wherein
• said reference level source alternately outputs said first and second reference levels in response to said oscillating signal, and
• said control circuit controls said charge/discharge circuit so that said charge/discharge circuit will alternately switch charge and discharge of said integrating capacitor in response to said oscillating signal, stop charge during a predetermined period within a charge period, and stop discharge during a predetermined period within a discharge period, wherein
• said charge/discharge circuit comprises:
• a first current source for supplying said current proportional to the voltage level of said input signal to said integrating capacitor;
• and
• a second current source for causing said current proportional to the voltage level of said input signal to flow from said integrating capacitor, and wherein
• said control circuit comprises:
• a stop switch installed on a path along which a current flows for charging or discharging said integrating capacitor;
• a first switch interposed between said first current source and stop switch;
• a second switch interposed between said second current source and stop switch and alternately closed and opened in association with phases opposite to phases with which said first switch is closed and opened;
• and
• a stop signal generation circuit for generating a stop signal, which becomes active during said predetermined period, in response to said oscillating signal, and said stop switch is opened in response to said stop signal.

A frequency-voltage converter for generating a voltage dependent on the frequency of an input oscillating signal, comprising:

• an integrating capacitor;
• a reset circuit for resetting the terminal voltage of said integrating capacitor at intervals of one cycle of said oscillating signal;
• a constant current source for charging said integrating capacitor with a constant current;
• a charge control circuit for controlling charge so that charge will be stopped during a predetermined period within a charge period within which said integrating capacitor is charged;
• and
• a sample and hold circuit for sampling and holding a voltage developed at said integrating capacitor at the end of said charge period within which said integrating capacitor is charged, wherein
• said reset circuit comprises:
• a square-wave signal generation circuit for generating a square-wave signal by comparing said input signal with a predetermined voltage;
• an edge pulse generation circuit for generating an edge pulse by detecting the leading edge or trailing edge of said square-wave signal;
• a delay circuit for delaying said edge pulse and outputting a delayed edge pulse;
• and
• a reset switch interposed between said integrating capacitor and a reset voltage source and closed in response to said delayed edge pulse.