Digital control for a microelectromechanical element

• US 9,722,521 B2
• Filed: 10/13/2011
• Issued: 08/01/2017
• Est. Priority Date: 11/23/2010
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Krayl, Oliver, Al Dibs, Mohamad Iyad, Wenzler, Axel
• Primary Examiner(s): Ismail, Shawki S
• Assistant Examiner(s): Imtiaz, Zoheb
• Application Number:
  US13/988,457
• Publication Number:
  US 20130293161A1
• Time in Patent Office: 2,119 Days
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: H02N 1/002 Electrostatic motors
• CPC Class Codes: H02P 13/00 Arrangements for controlling transformers, reactors or choke coils, for the purpose of obtaining a desired output

Abstract

A control circuit for a microelectromechanical element includes: a waveform generator, which is designed to generate a digital trigger signal for the microelectromechanical element, a modulator, which is designed to oversample the digital trigger signal, to subject the signal to a noise shaping, and to output the oversampled and noise-shaped digital trigger signal; and a digital driver device, which is designed to drive the microelectromechanical element using the oversampled and noise-shaped digital trigger signal.

Claims

1. A method for triggering a microelectromechanical element, comprising:

providing a digital trigger signal at a signal frequency which is below a predetermined cutoff frequency of an equivalent circuit of the microelectromechanical element, wherein the equivalent circuit includes a first input resistor, a first capacitor, a second capacitor, and a second resistor;

oversampling the digital trigger signal at a sampling frequency which is higher than twice the predetermined cutoff frequency;

noise-shaping of the oversampled digital trigger signal by shifting a noise which occurs during the oversampling to a frequency range above the predetermined cutoff frequency; and

driving the microelectromechanical element using the oversampled digital trigger signal, wherein the trigger signal does not have, at any time, frequency components corresponding to frequencies of a resonant mode of the microelectromechanical element.

2. The method as recited in claim 1, wherein the steps of oversampling and noise-shaping are carried out using a delta-sigma modulator.

3. The method as recited in claim 2, wherein a zero of a transfer function of an integrator of the delta-sigma modulator is set to a frequency of a resonant mode of the microelectromechanical element in a frequency range below the predetermined cutoff frequency.

8. The method of claim 1, wherein the frequency range which is below the predetermined cutoff frequency represents a useful range of the microelectromechanical element.

10. The method of claim 1, wherein the frequency range above the predetermined cutoff frequency represents an attenuation-dominated range of the micromechanical element.

4. A control circuit for a microelectromechanical element;

comprising;

a waveform generator configured to generate a digital trigger signal for the microelectromechanical element at a signal frequency which is below a predetermined cutoff frequency of an equivalent circuit of the microelectromechanical element, wherein the equivalent circuit includes a first input resistor, a first capacitor, a second capacitor, and a second resistor;

a modulator configured to (i) oversample the digital trigger signal at a sampling frequency which is higher than twice the predetermined cutoff frequency the digital trigger signal, (ii) noise-shape the oversampled digital trigger signal by shifting a noise which occurs during the oversampling to a frequency range above the predetermined cutoff frequency, and (iii) output the oversampled and noise-shaped digital trigger signal; and

a digital driver device configured to drive the microelectromechanical element using the oversampled and noise-shaped digital trigger signal during quasi-static operation, wherein the trigger signal does not have, at any time, frequency components corresponding to frequencies of a resonant mode of the microelectromechanical element.

5. The control circuit as recited in claim 4, wherein the modulator is a delta-sigma modulator.

6. The control circuit as recited in claim 5, wherein the microelectromechanical element is a capacitive actuator.

7. The control circuit as recited in claim 6, wherein a zero of a transfer function of an integrator of the delta-sigma modulator is set to a frequency of a resonant mode of the microelectromechanical element in a frequency range below the predetermined cutoff frequency.

9. The control circuit as recited in claim 4, wherein the frequency range which is below the predetermined frequency represents a useful range of the microelectromechanical element.

11. The control circuit as recited in claim 4, wherein the frequency range above the predetermined cutoff frequency represents an attenuation-dominated range of the micromechanical element.