Chopper-stabilized instrumentation amplifier for impedance measurement

Patent metadata

Field	Value
Publication number	US-9615744-B2
Application number	US-87255210-A
Country	US
Kind code	B2
Filing date	Aug 31, 2010
Priority date	Jan 31, 2007
Publication date	Apr 11, 2017
Grant date	Apr 11, 2017

Abstract

In general, this disclosure is directed to a mixer amplifier that can be utilized within a chopper stabilized instrumentation amplifier. The chopper stabilized instrumentation amplifier may be used for physiological signal sensing, impedance sensing, telemetry or other test and measurement applications. In some examples, the mixer amplifier may include a current source configured to generate a modulated current at a modulation frequency for application to a load to produce an input signal, an amplifier configured to amplify the input signal to produce an amplified signal, and a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the load.

First claim

The invention claimed is:

1. An electrical impedance sensing device comprising:
a current source configured to generate a modulated current at a modulation frequency for application to a biological load to produce an input signal;
an amplifier configured to amplify the input signal to produce an amplified signal;
a demodulator configured to demodulate the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load;
first implantable electrodes coupled to apply the modulated current across the biological load; and
second implantable electrodes coupled to sense the input signal produced across the biological load.

2. The sensing device of claim 1 , further comprising:
a modulator configured to modulate the output signal at the modulation frequency to produce a feedback signal; and
a feedback path that applies the feedback signal to the input signal.

3. The sensing device of claim 1 , wherein the current source comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current.

4. The sensing device of claim 1 ,
wherein the amplified signal is a current-mode signal,
wherein the demodulator is further configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce a current-mode demodulated signal, and
wherein the sensing device further comprises a current-to-voltage converter configured to perform a current-to-voltage conversion operation on the demodulated signal to produce a voltage-mode output signal indicating the impedance of the biological load.

5. The sensing device of claim 4 ,
wherein the current-to-voltage converter comprises a resistance configured to perform the current-to-voltage conversion operation on the current-mode demodulated signal to produce the voltage-mode output signal, and
wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

6. The sensing device of claim 1 ,
wherein the sensing device further comprises a resistance coupled between a node carrying the output signal and a node regulated at a common voltage, and
wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

7. The sensing device of claim 6 ,
wherein the amplifier comprises a transconductor, and
wherein the level of gain is determined at least in part by the resistance value of the resistance and a transconductance of the transconductor.

8. The sensing device of claim 1 ,
wherein the demodulator is further configured to demodulate an amplitude of the amplified signal at the modulation frequency to produce a demodulated signal, and
wherein the sensing device further comprises a low-pass filter configured to perform a low-pass filtering operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

9. The sensing device of claim 8 ,
wherein the low-pass filter comprises a resistance configured to assist in performing the low-pass filtering operation on the demodulated signal, and
wherein the amplifier is further configured to amplify the input signal at a level of gain that is determined at least in part by a resistance value of the resistance of the low-pass filter.

10. The sensing device of claim 9 ,
wherein the low-pass filter further comprises a capacitance, and
wherein the low-pass filter is further configured to perform the low-pass filtering operation on the demodulated signal with a corner frequency determined at least in part by the resistance value of the resistance and a capacitance value of the capacitance.

11. The sensing device of claim 9 , wherein the resistance of the low-pass filter is further configured to perform a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

12. The sensing device of claim 8 ,
wherein the low-pass filter comprises a resistance configured to assist in performing the low-pass filtering operation on the demodulated signal, and
wherein the resistance is further configured to perform a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

13. A biological impedance sensing device comprising:
means for applying a current modulated at a modulation frequency across a biological load to produce an input signal;
means for amplifying the input signal to produce an amplified signal;
means for demodulating the amplified signal at the modulation frequency to produce an output signal indicating an impedance of the biological load;
first implantable electrodes coupled to apply the modulated current across the biological load; and
second implantable electrodes coupled to sense the input signal produced across the biological load.

14. The sensing device of claim 13 , further comprising:
means for modulating the output signal at the modulation frequency to produce a feedback signal; and
means for applying the feedback signal to the input signal.

15. The sensing device of claim 13 , wherein the means for applying the modulated current comprises a voltage source and a switch that modulates a current produced by the voltage source to produce the modulated current.

16. The device of claim 13 , wherein the means for demodulating the amplified signal comprises means for demodulating an amplitude of the amplified signal at the modulation frequency to produce a demodulated signal, and wherein the device further comprises means for performing a low-pass filtering operation on the demodulated signal to produce the output signal indicating an impedance of the biological load.

17. The sensing device of claim 16 ,
wherein the means for performing the low-pass filtering operation on the demodulated signal comprises means for performing, with at least a resistance, the low-pass filtering operation on the demodulated signal, and
wherein the means for amplifying the input signal comprises means for amplifying the input signal at a level of gain that is determined at least in part by a resistance value of the resistance.

18. The sensing device of claim 17 , wherein the means for performing the low-pass filtering operation on the demodulated signal further comprises means for performing, with the resistance and a capacitance, the low-pass filtering operation on the demodulated signal with a corner frequency determined at least in part by the resistance value of the resistance and a capacitance value of the capacitance.

19. The sensing device of claim 17 , further comprising:
means for performing, with at least the resistance, a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

20. The sensing device of claim 16 , wherein the means for performing the low-pass filtering operation on the demodulated signal comprises:
means for performing, with at least a resistance, the low-pass filtering operation on the demodulated signal; and
means for performing, with at least the resistance, a current-to-voltage conversion operation on the demodulated signal to produce the output signal indicating the impedance of the biological load.

21. The sensing device of claim 13 ,

Assignees

• Denison Timothy J
• Santa Wesley A
• Medtronic Inc

Inventors

• Denison Timothy J
• Santa Wesley A

Classifications

• H03F3/387

  with semiconductor devices only · CPC title

• H03F2203/45534

  the FBC comprising multiple switches and being coupled between the LC and the IC · CPC title

• H03F2203/45264

  the dif amp comprising frequency or phase stabilisation means · CPC title

• H03F2203/45212

  the differential amplifier being designed to have a reduced offset · CPC title

• H03F2203/45028

  the differential amplifier amplifying transistors are folded cascode coupled transistors · CPC title