Reference voltage calibration apparatus in memory interface
Disclosed herein is a reference voltage calibration apparatus in a memory interface. The reference voltage calibration apparatus includes a first low-pass filter configured to receive a clock signal, a second low-pass filter configured to receive an inverted clock signal that is an inverted signal of the clock signal, a first comparator configured to compare an output of the first low-pass filter with a reference voltage, a second comparator configured to compare an output of the second low-pass filter with the reference voltage, an up/down counter configured to count upward or downward from output values of the first comparator and the second comparator, respectively, and a digital-to-analog converter configured to convert an up/down counter value into an analog signal, and then output the reference voltage, wherein the digital-to-analog converter applies a calibration voltage based on the reference voltage to the first low-pass filter and to the second low-pass filter.
1 . A reference voltage calibration apparatus in a memory interface, comprising:
a first low-pass filter configured to receive a clock signal;
a second low-pass filter configured to receive an inverted clock signal that is an inverted signal of the clock signal;
a first comparator configured to compare an output of the first low-pass filter with a reference voltage;
a second comparator configured to compare an output of the second low-pass filter with the reference voltage;
an up/down counter configured to count upward or downward from output values of the first comparator and the second comparator, respectively; and
a digital-to-analog converter configured to convert an up/down counter value into an analog signal, and then output the reference voltage,
wherein the digital-to-analog converter applies a calibration voltage based on the reference voltage to the first low-pass filter and to the second low-pass filter.
2 . The reference voltage calibration apparatus of claim 1 , wherein the calibration voltage has an intermediate value of a high signal and a low signal of the reference voltage.
3 . The reference voltage calibration apparatus of claim 1 , wherein each of the first low-pass filter and the second low-pass filter generates an output value based on the calibration voltage during an initialization period or a period in which a clock signal is not applied.
4 . The reference voltage calibration apparatus of claim 1 , wherein the first low-pass filter or the second low-pass filter comprises:
a first switch configured to turn on/off the clock signal or the inverted clock signal that is an input signal applied to a filter stage; and
the filter stage configured to allow a signal having a frequency lower than a predetermined value from the input signal to pass therethrough,
wherein the filter stage comprises:
a resistor having a first end to which the input signal is applied;
a capacitor connected between a second end of the resistor and a ground; and
a second switch connected to the second end of the resistor and configured to turn on/off the calibration voltage that is input from the digital-to-analog converter.
5 . The reference voltage calibration apparatus of claim 4 , wherein the second switch is turned on during an initialization period or the period in which the clock signal is not applied.
6 . The reference voltage calibration apparatus of claim 5 , wherein:
the filter stage is implemented using two or more filter stages, and
each of the filter stages is connected to a second end of a resistor in a previous filter stage.
7 . The reference voltage calibration apparatus of claim 6 , wherein the filter stage further comprises:
a first current source configured to output a current flowing from a voltage source to a connection node of the filter stage;
a second current source configured to output a current flowing from the connection node to a ground;
a third switch configured to turn on/off a connection between the first current source and the connection node; and
a fourth switch configured to turn on/off a connection between the second current source and the connection node.
8 . A low-pass filter in a reference voltage calibration apparatus, comprising:
a first switch configured to turn on/off a clock signal or an inverted clock signal that is an input signal applied to a filter stage; and
the filter stage configured to allow a signal having a frequency lower than a predetermined value from the input signal to pass therethrough,
wherein the filter stage comprises:
a resistor having a first end to which the input signal is applied;
a capacitor connected between a second end of the resistor and a ground; and
a second switch connected to the second end of the resistor and configured to turn on/off a calibration voltage that is input.
9 . The low-pass filter of claim 8 , wherein the calibration voltage has an intermediate value of a high signal and a low signal of a reference voltage.
10 . The low-pass filter of claim 8 , wherein the second switch is turned on during an initialization period or a period in which a clock signal is not applied.
11 . The low-pass filter of claim 10 , wherein:
the filter stage is implemented using two or more filter stages, and
each of the filter stages is connected to a second end of a resistor in a previous filter stage.
12 . The low-pass filter of claim 11 , wherein the filter stage further comprises:
a first current source configured to output a current flowing from a voltage source to a connection node of the filter stage;
a second current source configured to output a current flowing from the connection node to a ground;
a third switch configured to turn on/off a connection between the first current source and the connection node; and
a fourth switch configured to turn on/off a connection between the second current source and the connection node.