DIGITAL HIGH-PASS FILTER FOR A DISPLACEMENT DETECTION DEVICE OF A PORTABLE APPARATUS

• US 20080079594A1
• Filed: 09/28/2007
• Published: 04/03/2008
• Est. Priority Date: 03/31/2005
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Tronconi, Michele, Pasolini, Fabio, Chiesa, Enrico
• Granted Patent: US 7,783,449 B2
• Time in Patent Office: Days
• US Class Current: 340/669
• CPC Class Codes: G01P 15/0891 with indication of predetermined acceleration values G01P15/135 takes precedence
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: H03H 17/04 Recursive filters

Abstract

A digital high-pass filter has an input, an output, and a subtractor stage, having a first input terminal, a second input terminal and an output terminal. The first input terminal of the subtractor stage is connected to the input of the digital high-pass filter and the output terminal is connected to the output of the digital high-pass filter. A recursive circuit branch is connected between the output of the digital high-pass filter and the second input terminal of the subtractor stage. Within the recursive circuit branch are cascaded an accumulation stage, constituted by an integrator circuit, and a divider stage. The cutoff frequency of the digital high-pass filter is variable according to a dividing factor of the divider stage.

Claims

1. A digital high-pass filter comprising:

an input;

an output;

a subtractor stage, having a first input terminal and a second input terminal and an output terminal, said first input terminal being connected to said input of said digital high-pass filter and said output terminal being connected to said output of said digital high-pass filter; and

a recursive circuit branch connected between said output of said digital high-pass filter and said second input terminal of said subtractor stage, wherein said recursive circuit branch comprises an accumulation stage and a divider stage cascaded to one another.

2. The digital high-pass filter according to claim 1 wherein said divider stage performs a division by a variable dividing factor, having a value greater than 1.

3. The digital high-pass filter according to claim 2 wherein said dividing factor is a power of 2.

4. The digital high-pass filter according to claim 1 wherein said accumulation stage comprises an integrator circuit.

5. The digital high-pass filter according to claim 4, wherein said integrator circuit has a recursive accumulation structure having an own input terminal and an own output terminal, and comprising at least one adder block connected to said own input terminal, and at least one delay block connected to said adder block and to said own output terminal.

6. The digital high-pass filter according to claim 5 wherein said adder block has a first positive input and a second positive input and an output, said first positive input of said adder block being connected to said input terminal of said integrator stage, and said output of said adder block being connected to said output terminal of said integrator stage;

said delay block having an input connected to said output terminal of said integrator stage and an output connected to said second positive input of said adder block.

7. The digital high-pass filter according to claim 5, wherein said adder block has a first positive input and a second positive input and an output, said first positive input of said adder block being connected to said input terminal of said integrator stage, said second positive input of said adder block being connected to said output terminal of said integrator stage;

said delay block having an input connected to said output of said adder block and an output connected to said output terminal of said integrator stage.

8. The digital high-pass filter according to claim 1 wherein the subtractor stage and the recursive circuit branch are implemented in hardware using an application specific integrated circuit (ASIC).

9. The digital high-pass filter according to claim 1 wherein the subtractor stage and the recursive circuit branch are implemented via software using firmware stored in a microprocessor.

10. The digital high-pass filter according to claim 1 further comprising an adjuster coupled to the divider stage and structured to adjust a dividing factor of the dividing stage.

11. A displacement detection device, comprising:

an acceleration sensor generating a first acceleration signal corresponding to a first detection axis; and

a displacement detection circuit connected to said acceleration sensor and generating a first displacement-detection signal, said displacement detection circuit including a digital, first high-pass filter configured to reduce a continuous component of said first acceleration signal wherein said first high-pass filter includes;

an input;

an output;

a subtractor stage, having a first input terminal and a second input terminal and an output terminal, said first input terminal being connected to said input of said digital high-pass filter and said output terminal being connected to said output of said digital high-pass filter; and

a recursive circuit branch connected between said output of said digital high-pass filter and said second input terminal of said subtractor stage, wherein said recursive circuit branch comprises an accumulation stage and a divider stage cascaded to one another.

12. The displacement detection device according to claim 11 wherein said displacement detection circuit comprises a first comparator stage receiving said first acceleration signal and a first acceleration threshold, and generating said first displacement-detection signal, and wherein said first high-pass filter is disposed between said acceleration sensor and said first comparator stage.

13. The device according to claim 11, wherein said displacement detection circuit further comprises cutoff frequency modifying means connected to said first high-pass filter for adjusting the cutoff frequency of said digital high-pass filter, wherein said cutoff frequency modifying means includes varying a dividing factor of the divider stage of said first high-pass filter.

14. The device according to claim 11, wherein said displacement detection circuit is implemented as an ASIC and is integrated with said acceleration sensor within a single chip wherein said acceleration sensor is a MEMS sensor.

15. The device according to claim 11, further comprising a microprocessor connected to said acceleration sensor and wherein said displacement detection circuit is made in a firmware stored in said microprocessor, and said microprocessor and said acceleration sensor are integrated in a single chip, wherein said acceleration sensor is a MEMS sensor.

16. The device according to claim 11, wherein said acceleration sensor is a linear accelerometer with three detection axes further generating a second acceleration signal and a third acceleration signal, said first, second and third acceleration signals being correlated to a component of the acceleration along a respective detection axis;

and wherein said displacement detection circuit further comprises;

a second comparator stage and a third comparator stage, for comparing, respectively, said second acceleration signal and said third acceleration signal with said first acceleration threshold and generating a second displacement-detection signal and a third displacement-detection signal; and

second and third high-pass filters arranged, respectively, between said acceleration sensor and said second and third comparator stages, and configured to reduce continuous components, respectively, of said second and third acceleration signals.

17. A portable apparatus, comprising a displacement detection device that includes:

an acceleration sensor generating a first acceleration signal corresponding to a first detection axis; and

a displacement detection circuit connected to said acceleration sensor and generating a first displacement-detection signal, said displacement detection circuit comprising first high-pass filtering means configured to reduce a continuous component of said first acceleration signal wherein said first high-pass filtering means comprises a digital high-pass filter having an adjustable cutoff frequency.

18. The apparatus according to claim 17 wherein the portable apparatus further comprises a microprocessor, wherein said microprocessor is connected to an output of said displacement detection device for determining the displacement direction of said portable apparatus.

19. The apparatus according to claim 17, wherein said apparatus is one of a group consisting of laptops, PDAs, audio players, mobile phones, cameras, and videocameras.

20. A portable apparatus comprising:

an acceleration sensor for generating an acceleration signal corresponding to a detection axis; and

a displacement detection circuit operatively connected to the acceleration sensor and structured to generate a displacement-detection signal corresponding to the acceleration signal, wherein the displacement detection circuit is structured to eliminate a continuous component from the acceleration signal.

21. The portable apparatus of claim 20, further comprising:

a microprocessor communicatively coupled to an output of the displacement detection circuit for determining a displacement direction of the portable apparatus.

22. The portable apparatus according to claim 20 wherein the displacement detection circuit comprises:

a high-pass filter configured to eliminate the continuous component from the acceleration signal; and

an adjustment stage communicatively coupled to the high-pass filter and structured to vary a cutoff frequency associated with the high-pass filter.

23. The portable apparatus according to claim 22 wherein the high-pass filter comprises:

a subtractor stage having a first input terminal and a second input terminal and an output terminal, wherein the first input terminal is coupled to an input of the high-pass filter and the output terminal is connected to an output of the high-pass filter;

an accumulation stage;

a divider stage, wherein the accumulation stage and the divider stage are cascaded to form a recursive branch coupled between the output of the high-pass filter and the second input terminal of the subtractor stage.

24. The portable apparatus according to claim 23 wherein the divider stage is structured to perform division using a variable dividing factor that is adjusted via the adjustment stage, wherein the variable dividing factor controls the cutoff frequency of the high-pass filter.

25. The portable apparatus according to claim 22, wherein the displacement detection circuit comprises:

a storage element structured to store an acceleration threshold; and

a comparator coupled to an output of the high-pass filter and the storage element, and having first and second inputs structured to receive the first acceleration signal without the continuous component and the first acceleration threshold signal, respectively, wherein the comparator generates the displacement-detection signal based on a comparison of the signals on the first and second inputs.