Band pass filter and calibration method for band pass filter
View Patent ↗A band pass filter has a high pass filter into which an input signal is input; an amplifier having an inverting input terminal into which an output of the high pass filter is input, wherein the amplifier amplifies an input voltage between the inverting input terminal and a non-inverting input terminal and outputs an output signal to an output terminal; a first resistor connected between a non-inverting output terminal and the inverting input terminal of the amplifier; a first capacitor having a first terminal that is connected to the inverting input terminal; and an inverting amplifier that inverts a polarity of an output signal from the non-inverting output terminal of the amplifier and outputs the inverted signal to a second terminal of the capacitor.
1. A band pass filter, comprising:
a high pass filter into which an input signal is input;
an amplifier having an inverting input terminal into which an output of the high pass filter is input, wherein the amplifier amplifies an input voltage between the inverting input terminal and a non-inverting input terminal and outputs an output signal to an output terminal;
a first resistor connected between a non-inverting output terminal and the inverting input terminal of the amplifier;
a first capacitor having a first terminal that is connected to the inverting input terminal; and
an inverting amplifier that inverts a polarity of an output signal from the non-inverting output terminal of the amplifier and outputs the inverted signal to a second terminal of the first capacitor.
2. The band pass filter according to claim 1 , further comprising:
a variable capacitance capacitor, provided between the inverting input terminal of the amplifier and a reference voltage, in that a capacitance value thereof can be varied, and
a capacitance value variably setting unit configured to variably control the capacitance value of the variable capacitance capacitor to set the capacitance value such that a center frequency of the band pass filter reaches a desired frequency.
3. The band pass filter according to claim 2 , wherein the high pass filter comprises a second capacitor having a first terminal into which the input signal is input and a second resistor provided between a second terminal of the second capacitor and a reference potential, the second terminal being connected to the inverting input terminal of the amplifier,
the band pass filter further comprises first, second and third switches; and
a third resistor having a second terminal being connected to the second terminal of the second capacitor, wherein
the capacitance value variably setting unit configured to
convert the band pass filter into a capacitance value calibrating low pass filter, by controlling the first switch to make the input signal, inputting to the first terminal of the second capacitor, input to a first terminal of the third resistor, by controlling the second switch to disconnect the second resistor from the inverting input terminal, and by controlling the third switch to make a feedback loop of the first capacitor open,
form a ring oscillator by connecting the capacitance value calibrating low pass filters in series, and
set the capacitance value of the variable capacitance capacitor such that an oscillation frequency of the ring oscillator matches the desired center frequency.
4. The band pass filter according to claim 1 , wherein the high pass filter comprises a second capacitor having a first terminal into which the input signal is input and a second resistor provided between a second terminal of the second capacitor and a reference potential, the second terminal being connected to the inverting input terminal of the amplifier.
5. A band pass filter comprising:
a high pass filter into which a differential input signal is input;
an amplifier having a non-inverting input terminal and an inverting input terminal into which a differential output signal of the high pass filter is input, wherein the amplifier amplifies the differential input signal and outputs a differential output signal to an inverting output terminal and a non-inverting output terminal;
a first positive side resistor connected between the inverting output terminal and the non-inverting input terminal of the amplifier;
a first negative side resistor connected between the non-inverting output terminal and the inverting input terminal of the amplifier;
a first positive side capacitor connected between the non-inverting output terminal and the non-inverting input terminal of the amplifier; and
a first negative side capacitor connected between the inverting output terminal and the inverting input terminal of the amplifier.
6. The band pass filter according to claim 5 , further comprising:
a positive side variable capacitance capacitor, provided between the non-inverting input terminal of the amplifier and a reference voltage, in that a capacitance value thereof can be varied;
a negative side variable capacitance capacitor, provided between the inverting input terminal of the amplifier and the reference voltage, in that a capacitance value thereof can be varied; and
a capacitance value variably setting unit configured to variable control the capacitance values of the positive side and negative side variable capacitance capacitors to set the capacitance values such that a center frequency of the band pass filter reaches a desired frequency.
7. The band pass filter according to claim 6 , wherein the high pass filter comprises second positive side and negative side capacitors having respective first terminals into which the differential input signal is input, and second positive side, and negative side resistors provided between respective second terminals of the second positive side and negative side capacitors and a reference potential, the second terminals of the second positive side and negative side capacitors being connected respectively to the non-inverting input terminal and the inverting input terminal of the amplifier,
the band pass filter further comprises first, second and third switches; and
third positive side and negative side resistors having second terminals being respectively connected to the second terminals of the second positive side and negative side capacitors, wherein
the capacitance value variably setting unit configured to
convert the band pass filter into a capacitance value calibrating low pass filter, by controlling the first switches to make the input signal, inputting to the first terminals of the second positive side and negative side capacitors, input to first terminals of the third positive side and negative side resistors, by controlling the second switches to disconnect the second positive side and negative side resistors from the non-inverting and inverting input terminals, and by controlling the third switches to make feedback loops of the first positive side and negative side capacitors open,
form a ring oscillator by connecting the capacitance value calibrating low pass filters in series, and
set the capacitance values of the positive side and negative side variable capacitance capacitors such that an oscillation frequency of the ring oscillator matches the desired center frequency.
8. The band pass filter according to claim 5 , wherein the high pass filter comprises second positive side and negative side capacitors respectively having first terminals into which the differential input signal is input, and second positive side and negative side resistors provided between respective second terminals of the second positive side and negative side capacitors and a reference potential, the second terminals of the second positive side and negative side capacitors being connected respectively to the non-inverting input terminal and the inverting input terminal of the amplifier.
9. The band pass filter according to claim 5 , wherein the high pass filter comprises second positive side and negative side capacitors (C 1 ) respectively having first terminals into which the differential input signal is input, and second positive side and negative side resistors (R 1 ) provided between respective second terminals of the second positive side and negative side capacitors and a common mode voltage (VCM) of the differential input signal, the second terminals of the second positive side and negative side capacitors being connected respectively to the non-inverting input terminal and the inverting input terminal of the amplifier.
10. A calibration method for a band pass filter, comprising:
a high pass filter into which a differential input signal is input;
an amplifier having a non-inverting input terminal and an inverting input terminal into which a differential output signal of the high pass filter is input, wherein the amplifier amplifies the differential input signal and outputs a differential output signal to an inverting output terminal and a non-inverting output terminal;
a first positive side resistor connected between the inverting output terminal and the non-inverting input terminal of the amplifier;
a first negative side resistor connected between the non-inverting output terminal and the inverting input terminal of the amplifier;
a first positive side capacitor connected between the non-inverting output terminal and the non-inverting input terminal of the amplifier;
a first negative side capacitor connected between the inverting output terminal and the inverting input terminal of the amplifier;
a positive side variable capacitance capacitor that is provided between the non-inverting input terminal of the amplifier and a reference voltage such that a capacitance value thereof can be varied; and
a negative side variable capacitance capacitor that is provided between the inverting input terminal of the amplifier and the reference voltage such that a capacitance value thereof can be varied;
wherein the high pass filter comprises second positive side and negative side capacitors respectively having first terminals into which the differential input signal is input, and second positive side and negative side resistors provided between respective second terminals of the second positive side and negative side capacitors and a reference potential, the second terminals of the second positive side and negative side capacitors being connected respectively to the non-inverting input terminal and the inverting input terminal of the amplifier,
the band pass filter further having first, second and third switches; and
third positive side and negative side resistors having second terminals being respectively connected to the second terminals of the second positive side and negative side capacitors,
the calibration method comprising:
converting the band pass filter into a capacitance value calibrating low pass filter, by controlling the first switches to make the input signal, inputting to the first terminals of the second positive side and negative side capacitors, input to first terminals of the third positive side and negative side resistors, by controlling the second switches to disconnect the second positive side and negative side resistors from the non-inverting and inverting terminals, and by controlling the third switches to make feedback loops of the first positive side and negative side capacitors open,
form a ring oscillator by connecting the capacitance value calibrating low pass filters in series, and
set the respective capacitance values of the positive side and negative side variable capacitance capacitors such that an oscillation frequency of the constructed ring oscillator matches a desired center frequency.