Small-circuit-scale reference voltage generating circuit
A BGR circuit controls a switch circuit in synchronization with a clock signal from a control signal generating circuit and an inverted signal thereof, and thereby, alternately switches between a differential input terminal receiving a voltage VIM and a differential input terminal receiving a voltage VIP. An LPF circuit includes capacitive elements, a switch connected between an input node and each capacitive element, and a switch connected between an output node and each capacitive element. The LPF circuit controls ON/OFF of the switches in synchronization with a clock signal CLK, and thereby, calculates a moving average value of an output voltage of the BGR circuit in the most recent one clock cycle.
1. A reference voltage generating circuit, comprising:
a bandgap reference circuit generating a bandgap reference voltage; and
a filter circuit for smoothing said bandgap reference voltage, wherein
said bandgap reference circuit includes:
a reference voltage circuit that is configured to include an operational amplifier receiving a first input voltage at one differential input terminal and receiving a second input voltage at the other differential input terminal, and that generates said bandgap reference voltage based on an output voltage of said operational amplifier; and
a switch circuit for alternately switching between the differential input terminal receiving said first input voltage and the differential input terminal receiving said second input voltage, in synchronization with a clock signal, and
said filter circuit operates in synchronization with said clock signal and calculates a moving average value of said bandgap reference voltage in a most recent one clock cycle, wherein
said reference voltage circuit is configured to generate said bandgap reference voltage having a first voltage value when said clock signal is in a first logic level, and to generate said bandgap reference voltage having a second voltage value different from said first voltage value when said clock signal is in a second logic level,
said filter circuit includes:
a first capacitive element charged with said bandgap reference voltage having said first voltage value in a first clock cycle;
a second capacitive element charged with said bandgap reference voltage having said second voltage value in said first clock cycle;
a third capacitive element charged with said bandgap reference voltage having said first voltage value in a second clock cycle immediately before or after said first clock cycle; and
a fourth capacitive element charged with said bandgap reference voltage having said second voltage value in said second clock cycle, and
in said second clock cycle, said filter circuit outputs said bandgap reference voltage having a magnitude corresponding to an average value of charging voltages of said first and second capacitive elements, and in said first clock cycle, said filter circuit outputs said bandgap reference voltage having a magnitude corresponding to an average value of charging voltages of said third and fourth capacitive elements.
2. The reference voltage generating circuit according to claim 1 , wherein
said filter circuit further includes:
first to fourth switches connected between an input terminal and said first to fourth capacitive elements, respectively; and
fifth to eighth switches connected between an output terminal and said first to fourth capacitive elements, respectively, and
the reference voltage generating circuit further comprises
a control signal generating circuit generating a control signal for controlling ON/OFF of said first to eighth switches by using said clock signal.
3. The reference voltage generating circuit according to claim 1 , wherein
said reference voltage circuit further includes:
a first resistive element connected between an output terminal and the input terminal of said first input voltage, and having an adjustable resistance value; and
a second resistive element connected between said output terminal and the input terminal of said second input voltage, and having an adjustable resistance value.