Ultrasonic receiving circuit

• US 9,157,898 B1
• Filed: 02/21/2014
• Issued: 10/13/2015
• Est. Priority Date: 03/22/2010
• Status: Active Grant

• Current Assignee: Lutron Technology Company LLC
• Original Assignee: Lutron Electronics Company Incorporated (Lutron Electronics)
• Inventors: Steiner, James P.
• Primary Examiner(s): Nguyen, Tai T
• Application Number:
  US14/186,006
• Time in Patent Office: 599 Days
• Field of Search: 340/545.3, 340/539.1, 340/539.26, 340/540, 340/541, 340/552, 340/554, 340/565, 340/567, 367/94, 367/98, 367/135, 367/138
• US Class Current: 1/1
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01S 15/04 Systems determining presence of a target
• CPC Class Codes: G01S 7/521 Constructional features
• CPC Class Codes: G08B 13/1627 using Doppler shift detection circuits
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H05B 47/115 by determining the presence or movement of objects or living beings
• CPC Class Codes: Y02B 20/40 Control techniques providing energy savings, e.g. smart controller or presence detection

Abstract

An ultrasonic occupancy sensor for detecting presence or absence of an occupant in a space includes an ultrasonic receiving circuit having a synchronous rectifier that allows the circuit to detect small-magnitude ultrasonic waves having a Doppler shift. The sensor comprises an ultrasonic transmitter for transmitting ultrasonic waves at an ultrasonic operating frequency, and a controller that drives the transmitting circuit with complementary drive signals to control the ultrasonic operating frequency. The synchronous rectifier receives the drive signals from the controller and rectifies an amplified input signal to generate a rectified signal, which is filtered by a filter to generate a filtered signal. The controller receives the filtered signal and determines that the space is occupied if the magnitude of the filtered signal exceeds a threshold. The ultrasonic occupancy sensor may also include a low phase-noise oscillator circuit coupled to the controller for setting an internal operating frequency of the controller.

Claims

1. An ultrasonic occupancy sensor for detecting presence or absence of an occupant in a space, the occupancy sensor comprising:

an ultrasonic transmitting circuit comprising an ultrasonic transmitting element for transmitting ultrasonic waves;

an ultrasonic receiving circuit comprising an ultrasonic receiving element for receiving ultrasonic waves and generating an ultrasonic input signal, a synchronous rectifier for generating a rectified signal from the input signal, and a filter circuit for filtering the rectified signal to generate a filtered signal, the synchronous rectifier comprising at least one amplifier circuit and at least one analog switch coupled to an output of the amplifier circuit for forming the rectified signal; and

a controller operable to drive the ultrasonic transmitting circuit with a drive signal to control an ultrasonic transmission frequency of the transmitted ultrasonic waves, the controller operable to render the analog switch conductive and non-conductive in phase with the drive signal to form the rectified signal, the controller further operable to receive the filtered signal and to determine that the space is occupied in response to the filtered signal.

2. The sensor of claim 1, wherein the synchronous rectifier receives a first signal representative of the input signal.

3. The sensor of claim 2, wherein the synchronous rectifier comprises a first non-inverting amplifier and a first inverting amplifier both receiving the first signal, the synchronous rectifier further comprising a first analog switch coupled to an output of the first non-inverting amplifier and a second analog switch coupled to an output of the first inverting amplifier.

4. The sensor of claim 3, wherein the synchronous rectifier further comprises a second non-inverting amplifier and a second inverting amplifier both receiving the first signal, the synchronous rectifier further comprising a third analog switch coupled to an output of the second non-inverting amplifier and a fourth analog switch coupled to an output of the second inverting amplifier, the first and second analog switches controlled to be conductive and non-conductive on a complementary basis in phase with the drive signal, the third and fourth analog switches controlled to be conductive and non-conductive on a complementary basis 90 degrees out of phase with the drive signal.

5. The sensor of claim 4, wherein outputs of the first and second analog switches are summed together to form a first rectified signal, and outputs of the third and fourth analog switches are summed together to form a second rectified signal, the filter circuit comprising a first low-pass filter for filtering the first rectified signal to generate a first filtered signal, the filter circuit further comprising a second low-pass filter for filtering the second rectified signal to generate a second filtered signal, the controller operable to receive both of the first and second filtered signals and to determine that the space is occupied in response to the first and second filtered signals.

6. The sensor of claim 3, wherein the first and second analog switches are electrically coupled together and controlled to be conductive and non-conductive in phase with the drive signal and on a complementary basis, such that outputs of the analog switches are mixed together to form the rectified signal.

7. The sensor of claim 2, wherein the synchronous rectifier comprises a first and second amplifiers, the synchronous rectifier further comprising a first analog switch coupled to an output of the first amplifier and a second analog switch coupled to an output of the second amplifier, the first analog switch controlled to be conductive and non-conductive in phase with the drive signal to form a first rectified signal, the second analog switch is controlled to be conductive and non-conductive 90 degrees out of phase with the drive signal to form a second rectified signal, the filter circuit comprising a first low-pass filter for filtering the first rectified signal to generate a first filtered signal, the filter circuit further comprising a second low-pass filter for filtering the second rectified signal to generate a second filtered signal, the controller operable to receive both of the first and second filtered signals and to determine that the space is occupied in response to the first and second filtered signals.

8. The sensor of claim 2, further comprising:

a low phase-noise oscillator circuit coupled to the controller for setting an internal operating frequency of the controller that is approximately equal to the ultrasonic transmission frequency of the transmitted ultrasonic waves.

9. The sensor of claim 1, wherein the controller is operable to determine that the space is occupied if a magnitude of the filtered signal exceeds a threshold.

10. The sensor of claim 9, wherein the filtered signal exceeds the threshold when a received ultrasonic frequency of the received ultrasonic waves is different than the ultrasonic transmission frequency of the transmitted ultrasonic waves.

11. The sensor of claim 9, wherein the controller is operable to determine that the space is occupied if a magnitude of the filtered signal rises above an upper threshold or falls below a lower threshold.

12. The sensor of claim 1, wherein the filter circuit comprises an anti-aliasing filter, and the controller is operable to digitally filter the filtered signal from the filter prior to determining if the space is occupied.

13. An ultrasonic receiving circuit for detecting a presence or absence of an occupant in a space comprises:

an ultrasonic receiving element for generating an ultrasonic input signal;

a synchronous rectifier for generating a rectified signal from the input signal, the synchronous rectifier comprising at least one amplifier circuit and at least one analog switch coupled to an output of the amplifier circuit for forming the rectified signal; and

a filter circuit for filtering the rectified signal to generate a filtered signal;

wherein the analog switch is rendered conductive and non-conductive to form the rectified signal such that the filtered signal indicates the presence of the occupant in the space.

14. The circuit of claim 13, wherein the synchronous rectifier receives a first signal representative of the input signal, the synchronous rectifier further receiving a drive signal, the analog switch rendered conductive and non-conductive in phase with the drive signal to form the rectified signal.

15. The circuit of claim 14, wherein the synchronous rectifier comprises a first non-inverting amplifier and a first inverting amplifier both receiving the first signal, the synchronous rectifier further comprising a first analog switch coupled to an output of the first non-inverting amplifier and a second analog switch coupled to an output of the first inverting amplifier.

16. The circuit of claim 15, wherein the synchronous rectifier further comprises a second non-inverting amplifier and a second inverting amplifier both receiving the first signal, the synchronous rectifier further comprising a third analog switch coupled to an output of the second non-inverting amplifier and a fourth analog switch coupled to an output of the second inverting amplifier, the first and second analog switches controlled to be conductive and non-conductive on a complementary basis in phase with the drive signal, the third and fourth analog switches controlled to be conductive and non-conductive on a complementary basis 90 degrees out of phase with the drive signal.

17. The circuit of claim 16, wherein outputs of the first and second analog switches are summed together to form a first rectified signal, and outputs of the third and fourth analog switches are summed together to form a second rectified signal, the filter circuit comprising a first low-pass filter for filtering the first rectified signal to generate a first filtered signal, the filter circuit further comprising a second low-pass filter for filtering the second rectified signal to generate a second filtered signal, the first and second filtered signals indicating the presence of the occupant in the space.

18. The circuit of claim 15, wherein the first and second analog switches are electrically coupled together and controlled to be conductive and non-conductive in phase with the drive signal and on a complementary basis, such that outputs of the analog switches are mixed together to form the rectified signal.

19. The circuit of claim 15, wherein the synchronous rectifier receives two drive signals, the drive signals comprising square wave voltage coupled to the first and second analog switches for rendering the analog switches conductive and non-conductive on a complementary basis.

20. The circuit of claim 14, wherein the synchronous rectifier comprises a first and second amplifiers, the synchronous rectifier further comprising a first analog switch coupled to an output of the first amplifier and a second analog switch coupled to an output of the second amplifier, the first analog switch controlled to be conductive and non-conductive in phase with the drive signal to form a first rectified signal, the second analog switch is controlled to be conductive and non-conductive 90 degrees out of phase with the drive signal to form a second rectified signal, the filter circuit comprising a first low-pass filter for filtering the first rectified signal to generate a first filtered signal, the filter circuit further comprising a second low-pass filter for filtering the second rectified signal to generate a second filtered signal, the first and second filtered signals indicating the presence of the occupant in the space.

21. The circuit of claim 20, wherein the first and second amplifiers both comprise non-inverting amplifiers or both comprise inverting amplifiers.

22. The circuit of claim 14, wherein the at least one amplifier circuit of the synchronous rectifier comprises a non-inverting amplifier, the analog switch of the synchronous rectifier rendered conductive in response to the drive signal from the controller.

23. The circuit of claim 14, wherein the at least one amplifier circuit of the synchronous rectifier comprises an inverting amplifier, the analog switch of the synchronous rectifier rendered conductive in response to the inverse of the drive signal from the controller.

24. The circuit of claim 14, wherein the drive signal is characterized by low phase noise.

25. The circuit of claim 13, wherein the filtered signal indicates the presence of the occupant in the space if a magnitude of the filtered signal exceeds a threshold.

26. The circuit of claim 25, wherein the ultrasonic receiving element receives ultrasonic waves representative of whether the space is occupied or unoccupied, the filtered signal exceeding the threshold when the frequency of the received ultrasonic waves is different than the frequency of the drive signal.

27. The circuit of claim 13, wherein the filtered signal indicates the presence of the occupant in the space if the magnitude of the filtered signal rises above an upper threshold or falls below a lower threshold.

28. The circuit of claim 13, further comprising:

a second amplifier circuit for amplifying the input signal to generate an amplified signal, the synchronous rectifier receiving the amplified signal and generating the rectified signal, the second amplifier circuit comprising a non-linear amplifier operable to amplify the input signal when the magnitude of the input signal is small, and not to amplify the input signal when the magnitude of the input signal is large.