Cancellation of a baseline current signal via current subtraction within a linear relaxation oscillator-based current-to-frequency converter circuit

• US 9,737,248 B1
• Filed: 06/23/2016
• Issued: 08/22/2017
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: Verily Life Sciences LLC (Alphabet Inc.)
• Original Assignee: Verily Life Sciences LLC (Alphabet Inc.)
• Inventors: Otis, Brian, Pletcher, Nathan
• Primary Examiner(s): Cheng, Jacqueline
• Assistant Examiner(s): BLOCH, MICHAEL RYAN
• Application Number:
  US15/190,358
• Time in Patent Office: 425 Days
• Field of Search: None
• CPC Class Codes: A61B 5/0004 characterised by the type of physiological signal transmitted
• CPC Class Codes: A61B 5/002 Monitoring the patient using a local or closed circuit, e.g. in a room or building A61B5/0017 takes precedence
• CPC Class Codes: A61B 5/0022 Monitoring a patient using a global network, e.g. telephone networks, internet
• CPC Class Codes: A61B 5/14507 specially adapted for measuring characteristics of body fluids other than blood devices for taking samples of body liquids A61B10/0045
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1477 non-invasive
• CPC Class Codes: A61B 5/6821 Eye
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G02C 7/04 Contact lenses for the eyes disinfection or sterilisation of contact lenses A61L12/00
• CPC Class Codes: H03K 3/0377 Bistables with hysteresis, e.g. Schmitt trigger non-regenerative amplitude discriminators G01R19/165
• CPC Class Codes: H03K 4/502 the capacitor being charged from a constant-current source
• CPC Class Codes: H04B 1/40 Circuits

Abstract

This disclosure relates to systems and/or methods for subtracting in the current domain an output current primary signal from a primary sensor from an output current reference signal from a reference sensor to produce a frequency output signal indicative of the difference between the output current primary signal and the output current reference signal.

Claims

1. An eye-mountable device comprising:

a first sensor that produces a first current signal during measurement of at least one parameter, wherein the first current signal comprises a measurement current signal associated with the at least one parameter and a baseline current signal;

a second sensor that produces a second current signal during the measurement of the at least one parameter, wherein the second current signal comprises the baseline current signal and does not include the measurement current signal associated with the at least one parameter; and

a linear relaxation oscillator-based current-to-frequency converter comprising an integration capacitor and a plurality of switches, wherein the integration capacitor has a first terminal connected to the first and second sensors via the plurality of switches and has a second terminal connected to ground, wherein the linear relaxation oscillator-based current-to-frequency converter produces an output frequency signal having a frequency related to a net current corresponding to a difference between the first current signal and the second current signal, wherein the output frequency signal comprises alternating charging phases and discharging phases, wherein during the charging phases the switches connect the first terminal of the integration capacitor to the first and second sensors such that the net current flows into the integration capacitor, and wherein during the discharging phases the switches connect the first terminal of the integration capacitor to the first and second sensors such that the net current flows out from the integration capacitor.

2. The eye-mountable device of claim 1, wherein the first sensor is an electrochemical sensor.

3. The eye-mountable device of claim 2, wherein the second sensor is an electrochemical sensor.

4. The eye-mountable device of claim 1, wherein the baseline current signal varies over at least one of time, temperature, or voltage potential during measurement of the at least one parameter.

5. The eye-mountable device of claim 1, further comprising a processor programmed to analyze the output frequency signal to determine a glucose level.

6. The eye-mountable device of claim 1, further comprising a power component, wherein the power component includes at least one of a battery, a capacitor, a solar power source, a radio frequency power source, an electrochemical power source, a temperature power source, or a mechanically derived power source.

7. The eye-mountable device of claim 1, further comprising a transceiver and an antenna.

8. The eye-mountable device of claim 1, wherein the switches are controlled by a feedback voltage derived from a voltage on the integration capacitor.

9. The eye-mountable device of claim 8, wherein the linear relaxation oscillator-based current-to-frequency converter further comprises an amplifier that generates the feedback voltage from the voltage on the integration capacitor.

10. The eye-mountable device of claim 9, wherein the amplifier is a Schmitt trigger.

11. The eye-mountable device of claim 1, wherein the plurality of switches include a first switch configured to connect a current output of the first sensor to the integration capacitor, a second switch configured to connect a current output of the second sensor to the integration capacitor, a third switch configured to connect a current input of the first sensor to the integration capacitor, and a fourth switch configured to connect a current input of the second sensor to the integration capacitor.

12. The eye-mountable device of claim 11, wherein during the charging phases the first and fourth switches are closed and the second and third switches are open, and wherein during the discharging phases the second and third switches are closed and the first and fourth switches are open.