Oscillation circuit and semiconductor integrated circuit including the same

Abstract

An oscillation circuit including, a latch for generating an output signal based on a first signal and a second signal, an electric-charge charge/discharge unit which has first and second capacitors, and charges or discharges the first and second capacitors complementarily based on the output signal, a first comparator which compares a first voltage according to electric charge accumulated in the first capacitor and a first reference voltage, and outputs the first signal, a second comparator which compares a second voltage according to electric charge accumulated in the second capacitor and the first reference voltage, and outputs the second signal, and a control unit for controlling a timing, to compensate for variations of signals in the latch, the first comparator, and the second comparator, at which respective voltage levels of the first reference voltage and the first voltage match.

What is claimed is: 
     
         1 . An oscillation circuit comprising:
 a latch for generating an output signal based on a first signal and a second signal;   an electric-charge charge/discharge unit which has first and second capacitors, and charges or discharges the first and second capacitors complementarily based on the output signal;   a first comparator which compares a first voltage according to electric charge accumulated in the first capacitor and a first reference voltage, and outputs the first signal;   a second comparator which compares a second voltage according to electric charge accumulated in the second capacitor and the first reference voltage, and outputs the second signal; and   a control unit for controlling a timing, to compensate for variations of signals in the latch, the first comparator, and the second comparator, at which respective voltage levels of the first reference voltage and the first voltage match,   wherein the control unit controls the voltage level of the first reference voltage in accordance with the frequency of the output signal.   
     
     
         2 . The oscillation circuit according to  claim 1 , wherein the control unit further comprises a control voltage generation unit which generates a control voltage having a voltage level according to the frequency of the output signal of the latch. 
     
     
         3 . The oscillation circuit according to  claim 2 , wherein the control voltage generation unit further includes a constant current source and a plurality of switches which generates the control voltage having the voltage level according to the frequency of the output signal of the latch. 
     
     
         4 . The oscillation circuit according to  claim 3 , wherein the control unit further comprises an comparison voltage generation unit that includes an operational amplifier connected with a resistance element and a third capacitor to generate a comparison voltage according to a different between an average value of the control voltage from the control voltage generation unit and the first reference voltage. 
     
     
         5 . The oscillation circuit according to  claim 1 , wherein the first signal comprises a set signal and a second signal comprises a reset signal. 
     
     
         6 . The oscillation circuit according to  claim 1 , wherein the control unit increases the voltage level of the first reference voltage with an increase in the frequency of the output signal, and decreases the voltage level of the first reference voltage with a decrease in the frequency of the output signal. 
     
     
         7 . The oscillation circuit according to  claim 1 , wherein the control unit controls slew rates of the first and second voltages in accordance with the frequency of the output signal. 
     
     
         8 . The oscillation circuit according to  claim 1 , wherein the control unit controls the timing, to compensate for variations of signals in the latch, the first comparator, and the second comparator, at which respective voltage levels of the first reference voltage and the first voltage match and a timing, to compensate for variations of signals in the latch, the first comparator, and the second comparator, at which respective voltage levels of the first reference voltage and the second voltage match in response to a frequency of the output signal. 
     
     
         9 . The oscillation circuit according to  claim 1 , wherein the latch comprises an RS flip-flop. 
     
     
         10 . The oscillation circuit according to  claim 1 , wherein the control unit comprises:
 a control voltage generation unit for generating a control voltage according to the frequency of the output signal; and   a voltage control unit for generating a comparison voltage according to a difference between a second reference voltage and the control voltage, as the first reference voltage.   
     
     
         11 . The oscillation circuit according to  claim 10 , wherein the control voltage generation unit includes a first constant current source circuit for feeding a constant current and a switched capacitor resistor having a resistance value according to the frequency of the output signal, and generates the control voltage having a voltage level determined based on a current value of the current flowing through the first constant current source circuit and the resistance value of the switched capacitor resistor. 
     
     
         12 . An oscillation circuit comprising:
 a latch for generating an output signal based on a first signal and a second signal;   an electric-charge charge/discharge unit which has first and second capacitors, and charges or discharges the first and second capacitors complementarily based on the output signal;   a first comparator which compares a first voltage according to electric charge accumulated in the first capacitor and a first reference voltage, and outputs the first signal;   a second comparator which compares a second voltage according to electric charge accumulated in the second capacitor and the first reference voltage, and outputs the second signal; and   a control unit for controlling a timing at which respective voltage levels of the first reference voltage and the first voltage match and a timing at which respective voltage levels of the first reference voltage and the second voltage match in accordance with a frequency of the output signal,   wherein the control unit includes a control voltage generation unit for generating a control voltage according to the frequency of the output signal and a voltage control unit for generating a comparison voltage according to a difference between a second reference voltage and the control voltage, as the first reference voltage.   
     
     
         13 . The oscillation circuit according to  claim 12 , wherein the electric-charge charge/discharge unit further comprises a second constant current source circuit for feeding a constant current and a switch unit for controlling continuity between the second constant current source circuit and the first capacitor, continuity between the second constant current source circuit and the second capacitor, continuity between a first power source and the first capacitor, and continuity between the first power source and the second capacitor, based on the output signal. 
     
     
         14 . The oscillation circuit according to  claim 12 , wherein the electric-charge charge/discharge unit further generates the control voltage having a voltage level determined based on a current value of the current flowing through the second constant current source circuit and a resistance value of a switched capacitor resistor comprised of the switch unit and the first and second capacitors. 
     
     
         15 . The oscillation circuit according to  claim 12 , wherein the voltages to the first and second capacitors are supplied to inverting input terminals of the first and second comparators respectively, and a comparison voltage is supplied to non-inverting input terminals of the first and second comparators. 
     
     
         16 . An oscillation circuit comprising:
 a latch for generating an output signal based on a first signal and a second signal;   an electric-charge charge/discharge unit which includes first and second capacitors, and charges or discharges the first and second capacitors complementarily based on the output signal, the electric-charge/discharge unit generates a control voltage according to the frequency of the output signal;   a first comparator which compares a first voltage according to electric charge accumulated in the first capacitor and a first reference voltage, and outputs the first signal;   a second comparator which compares a second voltage according to electric charge accumulated in the second capacitor and the first reference voltage, and outputs the second signal; and   a control unit for controlling a timing at which respective voltage levels of the first reference voltage and the first voltage match and a timing at which respective voltage levels of the first reference voltage and the second voltage match in accordance with a frequency of the output signal.   
     
     
         17 . The oscillation circuit according to  claim 16 , wherein the control unit includes a control voltage generation unit for generating a control voltage according to the frequency of the output signal and a voltage control unit for controlling slew rates of the first and second voltages in accordance with a difference between a second reference voltage as the first reference voltage and the control voltage. 
     
     
         18 . The oscillation circuit according to  claim 16 , wherein the control voltage generation unit includes a first constant current source circuit for feeding a constant current and a switched capacitor resistor having a resistance value according to the frequency of the output signal, and generates the control voltage having a voltage level determined based on a current value of the current flowing through the first constant current source circuit and the resistance value of the switched capacitor resistor. 
     
     
         19 . The oscillation circuit according to  claim 16 , wherein the voltage control unit generates a comparison voltage according to a difference between the second reference voltage and the control voltage,
 wherein the electric-charge charge/discharge unit further includes a variable current source circuit for feeding a current according to the comparison voltage and a switch unit for controlling continuity between the variable current source circuit and the first capacitor, controlling continuity between the variable current source circuit and the second capacitor, continuity between a first power source and the first capacitor, and continuity between the first power source and the second capacitor, based on the output signal, and   wherein the first and second capacitors comprise variable capacitors having capacitance values according to the comparison voltage.   
     
     
         20 . A PLL (Phase-locked loop) comprising:
 the oscillation circuit according to  claim 16 .