Apparatus and methods for gyroscope signal demodulation
Apparatus and methods for gyroscope signal demodulation are disclosed herein. In certain embodiments, a demodulation circuit for a microelectromechanical systems (MEMS) gyroscope includes a switched resistor filter that samples a gyroscope signal received from a microelectromechanical sensor. The switched resistor filter provides sampling with a controlled duty cycle and noise bandwidth limit to achieve high signal-to-noise ratio (SNR) performance.
1 . A demodulation circuit for a gyroscope, the demodulation circuit comprising:
a plurality of switches configured to receive an amplitude modulated (AM) gyroscope signal;
an output capacitor coupled to the plurality of switches, wherein the output capacitor is configured to output a demodulated gyroscope signal; and
a clock duty cycle control circuit configured to control a duty cycle of the plurality of switches, the plurality of switches comprising a first switch connected between a first input node and a first output node and controlled by a first switch control signal from the clock duty cycle control circuit, a second switch connected between the first input node and a second output node and controlled by a second switch control signal from the clock duty cycle control circuit, a third switch connected between a second input node and the second output node and controlled by the first switch control signal, and a fourth switch connected between the second input node and the first output node and controlled by the second switch control signal.
2 . The demodulation circuit of claim 1 , further comprising a high pass filter configured to filter the AM gyroscope signal prior to being received by the plurality of switches.
3 . The demodulation circuit of claim 2 , further comprising an amplifier configured to amplify the AM gyroscope signal prior to being filtered by the high pass filter.
4 . The demodulation circuit of claim 1 , further comprising a low pass filter configured to filter the demodulated gyroscope signal, wherein the low pass filter comprises the output capacitor and a resistor connected between the output capacitor and the plurality of switches.
5 . The demodulation circuit of claim 1 , wherein the clock duty cycle control circuit is configured to control a duty cycle of the first switch control signal and a duty cycle of the second switch control signal to be less than or equal to one quarter.
6 . The demodulation circuit of claim 1 , wherein a first end of the output capacitor is directly connected to the first output node, and a second end of the output capacitor is directly connected to the second output node.
7 . The demodulation circuit of claim 1 , further comprising a first low pass filtering resistor connected between a first end of the output capacitor and the first output node, and a second low pass filtering resistor connected between a second end of the output capacitor and the second output node.
8 . A method of signal demodulation for a gyroscope, the method comprising:
receiving an amplitude modulated (AM) gyroscope signal as an input to a plurality of switches;
outputting a demodulated gyroscope signal from an output capacitor coupled to the plurality of switches; and
controlling a duty cycle of the plurality of switches using a clock duty cycle control circuit, the plurality of switches comprising a first switch connected between a first input node and a first output node and controlled by a first switch control signal from the clock duty cycle control circuit, a second switch connected between the first input node and a second output node and controlled by a second switch control signal from the clock duty cycle control circuit, a third switch connected between a second input node and the second output node and controlled by the first switch control signal, and a fourth switch connected between the second input node and the first output node and controlled by the second switch control signal.
9 . The method of claim 8 , further comprising filtering the AM gyroscope signal prior to being received by the plurality of switches using a high pass filter.
10 . The method of claim 9 , further comprising amplifying the AM gyroscope signal prior to being filtered by the high pass filter using an amplifier.
11 . A gyroscope demodulation system comprising:
a microelectromechanical sensor configured to output an amplitude modulated (AM) gyroscope signal; and
a demodulation circuit comprising:
a plurality of switches configured to receive the AM gyroscope signal;
an output capacitor coupled to the plurality of switches, wherein the output capacitor is configured to output a demodulated gyroscope signal; and
a clock duty cycle control circuit configured to control a duty cycle of the plurality of switches, the plurality of switches comprising a first switch connected between a first input node and a first output node and controlled by a first switch control signal from the clock duty cycle control circuit, a second switch connected between the first input node and a second output node and controlled by a second switch control signal from the clock duty cycle control circuit, a third switch connected between a second input node and the second output node and controlled by the first switch control signal, and a fourth switch connected between the second input node and the first output node and controlled by the second switch control signal.
12 . The gyroscope demodulation system of claim 11 , further comprising an analog-to-digital converter (ADC) configured to generate a multi-bit digital output signal based on digitizing the demodulated gyroscope signal.
13 . The gyroscope demodulation system of claim 11 , wherein the demodulation circuit further comprises a high pass filter configured to filter the AM gyroscope signal prior to being received by the plurality of switches.
14 . The gyroscope demodulation system of claim 13 , wherein the demodulation circuit further comprises an amplifier configured to amplify the AM gyroscope signal prior to being filtered by the high pass filter.
15 . The gyroscope demodulation system of claim 11 , wherein the demodulation circuit further comprises a low pass filter configured to filter the demodulated gyroscope signal, wherein the low pass filter comprises the output capacitor and a resistor connected between the output capacitor and the plurality of switches.
16 . The gyroscope demodulation system of claim 11 , wherein a signal path from an output of the microelectromechanical sensor to the output capacitor is fully differential.
17 . The gyroscope demodulation system of claim 11 , wherein a first end of the output capacitor is directly connected to the first output node, and a second end of the output capacitor is directly connected to the second output node.
18 . The gyroscope demodulation system of claim 11 , further comprising a first low pass filtering resistor connected between a first end of the output capacitor and the first output node, and a second low pass filtering resistor connected between a second end of the output capacitor and the second output node.
19 . The method of claim 8 , further comprising using the clock duty cycle control circuit to control a duty cycle of the first switch control signal and a duty cycle of the second switch control signal to be less than or equal to one quarter.
20 . The method of claim 8 , further comprising providing low pass filtering using a first low pass filtering resistor connected between a first end of the output capacitor and the first output node, and using a second low pass filtering resistor connected between a second end of the output capacitor and the second output node.