In a delay circuit for inputting square waves, fluctuations in the amount of delay brought about by noise pulses present in input signals are reduced. A switch (SW 3 ) is controlled by an output signal (Vdo) from a Schmitt comparator, and selects either an electric current source for supplying a charging current to a capacitor (Cst) or an electric current source for supplying a discharging current. A current supply from the selected electric current source is turned on/off by controlling switches (SW 1 , SW 2 ) using an input signal (Vdi). The Schmitt comparator switches the level of Vdo in accordance with a voltage of Cst. The charging current is supplied to Cst when Vdi is H level at rising edge of Vdi, and the discharging current is supplied to Cst when Vdi is L level at trailing edge of Vdi.
1. A delay circuit for delaying and switching the level of an output signal relative to the switching between two levels in a single input signal, wherein:
in a period in which the output signal is at a first output level correlated with a first input level of the input signal, a predetermined quantity to be evaluated is increased according to an integrated value of a period in which the input signal is at a second input level, and the output signal is switched from the first output level to the second output level when the quantity to be evaluated exceeds a predetermined upper threshold; and
in a period in which the output signal is at a second output level correlated with the second input level, the quantity to be evaluated is reduced according to the integrated value of a period in which the input signal is at a first input level, and the output signal is switched from the second output level to the first output level when the quantity to be evaluated declines below a lower threshold set lower than the upper threshold.
2. The delay circuit of claim 1 , comprising:
a Schmitt trigger comparator for setting the upper threshold and the lower threshold for an input voltage, and outputting the output signal;
a capacitor for inputting a voltage that corresponds to an amount of charge to the Schmitt trigger comparator; and
a charge/discharge circuit for alternatively outputting a charging current to charge the capacitor and a discharging current to discharge the capacitor; wherein the charge/discharge circuit selectively outputs the charging current in a period in which the output signal is at the first output level and the input signal is at the second input level; and
wherein the charge/discharge circuit selectively outputs the discharging current in a period in which the output signal is at the second output level and the input signal is at the first input level.
3. The delay circuit of claim 2 , the charge/discharge circuit having:
a charging current source for generating the charging current; a discharging current source for generating the discharging current;
a charge/discharge selection switch provided between the capacitor and the charging current source and discharging current source, and used to connect the charging current source and the capacitor in a period in which the output signal is at the first output level, and to connect the discharging current source and the capacitor in a period in which the output signal is at the second output level;
a charge control switch connected in series between the charging current source and the charge/discharge selection switch, and used to selectively establish an on-state in a period in which the input signal is at the second input level; and
a discharge control switch connected in series between the discharging current source and the charge/discharge switch, and used to selectively establish the on-state in a period in which the input signal is at the first input level.