EP-4737851-A1 - ANALOG DEMODULATION USING FULL-WAVE RECTIFICATION AND OVERSAMPLING ADC

EP4737851A1EP 4737851 A1EP4737851 A1EP 4737851A1EP-4737851-A1

Abstract

The disclosure relates to a circuitry and a method for extracting a digitized DC voltage value representing a magnitude of a discrete-time signal received from a discrete-time system. A first full-wave rectifier performs a full-wave rectification of the discrete-time signal to obtain a full-wave rectified signal, and an oversampling analog-to-digital converter digitizes the full-wave rectified signal to obtain a bitstream. The oversampling ADC comprises a second-order or higher order delta-sigma modulator and a filter. The filter is configured to filter the bitstream to extract the digitized DC voltage value.

Inventors

AALTONEN, LASSE

Assignees

Murata Manufacturing Co., Ltd.

Dates

Publication Date: 20260506
Application Date: 20241031

Claims (20)

A circuitry for extracting a digitized DC voltage value representing a magnitude of a discrete-time signal received from a discrete-time system, characterized in that the circuitry comprises: - a first full-wave rectifier configured to perform a full-wave rectification of the discrete-time signal to obtain a full-wave rectified signal, - an oversampling analog-to-digital converter, ADC, configured to digitize the full-wave rectified signal to obtain a bitstream, wherein the oversampling ADC comprises a second-order or higher order delta-sigma modulator and a filter, and wherein the filter is configured to filter the bitstream to extract the digitized DC voltage value.
The circuitry according to claim 1, further comprising: - a switched capacitor amplifier configured to amplify the discrete-time signal, or - a high-pass filter with a switched capacitor feedback configured to amplify the discrete-time signal.
The circuitry according to claim 1 or 2, further comprising: - a second full-wave rectifier configured to perform a second full-wave rectification of the discrete-time signal to obtain a full-wave rectified quadrature signal, and - a quadrature circuitry comprising: - a second oversampling analog-to-digital converter, ADC, configured to digitize the full-wave rectified quadrature signal to obtain digital quadrature signal data, or - a switched-capacitor stage configured to obtain samples of the full-wave rectified quadrature signal to obtain an analog quadrature signal.
The circuitry according to claim 3, wherein the digital quadrature signal data or the analog quadrature signal is configured to be used for at least one of: - cancelling of quadrature errors from an angular rate signal, - electrostatic quadrature compensation, and - monitoring functional safety capable sensor.
The circuitry according to any one of claims 1 to 4, wherein - the discrete-time signal is an amplitude-modulated AC voltage signal with a carrier frequency, and - an output transducer of the discrete-time system producing the discrete-time signal, and the oversampling ADC are operated with the same sample rate, and - a ratio R between frequencies of the sample rate and the carrier frequency is any one of: 8, 6, 32, and 64.
The circuitry according to claim 5, wherein the filter is a decimation filter and a decimation ratio applied by the decimation filter is at least equal to the ratio R.
The circuitry according to claim 5 or 6, wherein an oversampling ratio OSR is a ratio of digital data rate after decimation filtering by the decimation filter and the sample rate, and a ratio OSR/R is 2 X where x is an integer at least -1, preferably at least 0, and most preferably at least 1.
The circuitry according to any one of claims 1 to 7, wherein the discrete-time system is a sense resonator of a vibratory MEMS gyroscope with an/the output transducer configured to obtain discrete-time samples to generate the discrete-time signal, and wherein the discrete-time signal represents a position of a sense mass of the sense resonator in an open sense loop of the vibratory MEMS gyroscope.
The circuitry according to claim 8, wherein the discrete-time signal is generated by sampling, by the output transducer, a Coriolis signal of the sense resonator of the vibratory MEMS gyroscope.
The circuitry according to claim 8 or 9, wherein the discrete-time signal represents the position of the sense mass of the sense resonator in a closed force feedback loop of the vibratory MEMS gyroscope, and wherein the force feedback loop comprises a force feedback circuitry configured to generate a force feedback signal based on the discrete-time signal.
A method for extracting a digitized DC voltage value representing a magnitude of a discrete-time signal received from a discrete-time system, characterized in that the method comprises: - performing a first full-wave rectification to the discrete-time signal to obtain a full-wave rectified signal, - digitizing the full-wave rectified signal by an oversampling analog-to-digital converter, ADC, comprising a second-order or higher order delta-sigma modulator, to obtain a bitstream, and - filtering the bitstream by a filter configured to extract the digitized DC voltage value.
The method according to claim 11, further comprising: - amplifying the discrete-time signal by a switched capacitor amplifier, or - amplifying the discrete-time signal by a high-pass filter with a switched capacitor feedback.
The method according to claim 11 or 12, further comprising: - performing a second full-wave rectification of the discrete-time signal by a second full-wave rectifier to obtain a full-wave rectified quadrature signal, and - performing a second digitizing of the full-wave rectified quadrature signal by a second oversampling ADC to obtain digital quadrature signal data, or - obtaining samples of the full-wave rectified quadrature signal by a switched capacitor stage to obtain an analog quadrature signal.
The method according to claim 13, comprising using the digital quadrature signal data or the analog quadrature signal for at least one of: - cancelling of quadrature errors from an angular rate signal, - electrostatic quadrature compensation, and - monitoring functional safety capable sensor.
The method according to any one of claims 11 to 14, wherein - the discrete-time signal is an amplitude-modulated AC voltage signal with a carrier frequency, and - wherein the method comprises operating an output transducer of the discrete-time system for producing the discrete-time signal, and the oversampling ADC with the same sample rate, and - wherein a ratio R between frequencies of the sample rate and the carrier frequency is any one of: 8, 6, 32, and 64.
The method according to claim 15, wherein the filter is a decimation filter, and a decimation ratio applied by the decimation filter is at least equal to the ratio R.
The method according to claim 15 or 16, wherein an oversampling ratio OSR is a ratio of digital data rate after decimation filtering by the decimation filter and the sample rate, and a ratio OSR/R is 2 X where x is an integer at least -1, preferably at least 0, and most preferably at least 1.
The method according to any one of claims 11 to 17, wherein the discrete-time system is a sense resonator of a vibratory MEMS gyroscope with the output transducer, and the discrete-time signal represents a position of a sense mass of the sense resonator in an open sense loop of the vibratory MEMS gyroscope.
The method according to claim 18, comprising generating the discrete-time signal by sampling, by the output transducer, a Coriolis signal of the sense resonator of the vibratory MEMS gyroscope.
The method according to claim 18 or 19, wherein the discrete-time signal represents the position of the sense mass of the sense resonator in a closed force feedback loop of the vibratory MEMS gyroscope, wherein the method comprises: - generating, by a force feedback circuitry, a force feedback signal based on the discrete-time signal.

Description

FIELD OF THE DISCLOSURE The present disclosure relates to a method and circuitries for analog demodulation, and particularly to method and circuitries for analog demodulation of discrete-time signals. BACKGROUND OF THE DISCLOSURE MEMS gyroscopes use the Coriolis effect to measure angular velocity. A mass element is driven into oscillating movement by an actuating drive force. This oscillation may be called "drive oscillation" or "primary oscillation", and it may be said that the mass element moves in a "primary oscillation mode". This movement can be either linear oscillation along a drive axis as illustrated in Figure 1A, or rotational oscillation about a drive axis as illustrated in Figure 1B. The actuating force which maintains the drive oscillation can be generated, for example, by an electrostatic (capacitive) or piezoelectric actuator. The actuator may also be called a force transducer or an input transducer. The electrical signal which controls this actuator may be called a drive signal. When the gyroscope containing the mass element in drive oscillation is subject to an angular rotation rate Ω about an input axis which is perpendicular to the drive axis, the mass element is driven into a second oscillation mode by the Coriolis force. This oscillation may be called "sense oscillation" or "secondary oscillation", and it may be said that the mass element moves in a "secondary oscillation mode". This sense oscillation can be either linear oscillation along a sense axis, or rotational oscillation about a sense axis. The sense axis may also be referred to as a secondary axis or as a detection axis, and the sense oscillation may also be referred to as a secondary oscillation or as a detection oscillation. If the primary oscillation is linear, the Coriolis force driven sense oscillation is typically linear but may alternatively be coupled to be rotational. If the primary oscillation is rotational, then the Coriolis force driven sense oscillation is typically rotational but may alternatively be coupled to be linear. MEMS vibratory gyroscopes have typically one drive axis on or about which the mass element called drive resonator, also referred to as a proof mass, oscillates. A large mechanical oscillation amplitude of the drive resonator is important to maximize the Coriolis signal. Coriolis force appears when an inertial reference frame of the oscillating MEMS vibratory gyroscope and its drive resonator is rotated about the input axis that is orthogonal to the drive axis. Rotation couples the drive oscillation in the direction of the sense axis, that is orthogonal to both the drive axis and the input axis. Coriolis force FCOR is caused according to formula: FCOR=2∗ΩvDRV∗mDRV, where Ω is the rotation rate about the input axis, and vDRV is the velocity and mDRV is the mass of the drive resonator. Figure 2 illustrates a high level schematic of an exemplary vibratory MEMS gyroscope. An electro-mechanical MEMS resonator 50 may be characterized by the two main motions: primary and secondary motion. The MEMS resonator 50 may comprise a single moving MEMS mass in a single MEMS element capable for both primary and secondary motions, or it may comprise two or more MEMS elements and moving masses. For simplicity, figure 2 illustrates a resonator with two MEMS elements, a drive resonator 51 and a sense resonator 52, the latter of which may also be called as a detection element or a sensing element. At least one primary mass of the drive resonator 51 is driven into the drive oscillation with a closed primary drive loop, which includes a primary analog front end circuitry (primary AFE) 61, a primary loop circuitry 100 and a primary analog back end circuitry (primary ABE) 71. The primary loop circuitry 100 may be analog or digital. The Coriolis force FCOR due to angular velocity Ω effecting the primary mass(es) causes secondary, detection movement of at least one secondary mass of the secondary element. As known in the art, detection movement of the at least one secondary mass may be mechanically coupled from the at least one primary resonator in various ways, so that the detection movement of the secondary mass to be similar to or different from the Coriolis force driven sense oscillation. A linear sense oscillation may be conveyed into a linear detection movement or into a rotational detection movement. A rotational detection oscillation may be conveyed into a rotational detection movement or into a linear detection movement. The movement of the secondary mass(es) of the secondary element is detected by a detection circuitry, which in this non-limiting example includes a secondary analog front end circuitry (secondary AFE) 62, a secondary loop circuitry 200 and optionally a secondary analog back end circuitry (secondary ABE) 63. The detection circuitry produces an "Angular Velocity Out" signal indicating amount of angular velocity Ω about the input axis detected by the vibratory MEMS gyroscope. In a simplified implementa