U.S. patent application number 14/683338 was filed with the patent office on 2015-10-15 for measuring electrode impedance in an impedance measurement circuit.
The applicant listed for this patent is Texas Instruments Incorporated. Invention is credited to Hussam Ahmed, Sandeep Kesrimal Oswal, Anand Hariraj Udupa, Jagannathan Venkataraman.
Application Number | 20150293045 14/683338 |
Document ID | / |
Family ID | 54264890 |
Filed Date | 2015-10-15 |
United States Patent
Application |
20150293045 |
Kind Code |
A1 |
Udupa; Anand Hariraj ; et
al. |
October 15, 2015 |
MEASURING ELECTRODE IMPEDANCE IN AN IMPEDANCE MEASUREMENT
CIRCUIT
Abstract
The disclosure provides a circuit for impedance measurement. The
circuit includes an excitation source coupled between a first set
of input switches. An impedance network is coupled between the
first set of input switches and a first set of output switches. The
impedance network includes a body impedance and a plurality of
electrode impedances. A sense circuit is coupled to the first set
of output switches. The sense circuit measures the body impedance
and at least one electrode impedance of the plurality of electrode
impedances.
Inventors: |
Udupa; Anand Hariraj;
(Bangalore, IN) ; Venkataraman; Jagannathan;
(Bangalore, IN) ; Ahmed; Hussam; (Calicut, IN)
; Oswal; Sandeep Kesrimal; (Bangalore, IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Texas Instruments Incorporated |
Dallas |
TX |
US |
|
|
Family ID: |
54264890 |
Appl. No.: |
14/683338 |
Filed: |
April 10, 2015 |
Current U.S.
Class: |
324/692 |
Current CPC
Class: |
A61B 5/6898 20130101;
A61B 5/7221 20130101; A61B 5/0535 20130101; A61B 2560/0468
20130101; A61B 5/0537 20130101; A61B 5/053 20130101 |
International
Class: |
G01N 27/04 20060101
G01N027/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2014 |
IN |
1926/CHE/2014 |
Claims
1. A circuit comprising: an excitation source coupled between a
first set of input switches; an impedance network coupled between
the first set of input switches and a first set of output switches,
the impedance network having a body impedance and a plurality of
electrode impedances; and a sense circuit coupled to the first set
of output switches, the sense circuit configured to measure the
body impedance and at least one electrode impedance of the
plurality of electrode impedances.
2. The circuit of claim 1, wherein the sense circuit is configured
to generate an indication signal when at least one electrode
impedance of the plurality of electrode impedances is above a
defined threshold.
3. The circuit of claim 1, wherein the sense circuit is configured
to determine a an accurate value of the body impedance when each
electrode impedance of the plurality of electrode impedances is
below the defined threshold, and wherein the sense circuit is
configured to determine the accurate value of the body impedance
from the body impedance and the plurality of electrode
impedances.
4. The circuit of claim 1 further comprising: a second set of input
switches coupled in parallel to the first set of input switches,
wherein the excitation source is coupled between the second set of
input switches; and a second set of output switches coupled between
the impedance network and the sense circuit.
5. The circuit of claim 1, wherein the plurality of electrode
impedances comprises: a first input electrode impedance coupled to
a first excitation terminal; a second input electrode impedance
coupled to a second excitation terminal; wherein the body impedance
is coupled between the first input electrode impedance and the
second input electrode impedance; a first output electrode
impedance coupled to a first sense terminal; and a second output
electrode impedance coupled to a second sense terminal.
6. The circuit of claim 1, wherein the first set of input switches
comprises: a first input switch coupled between the excitation
source and the first excitation terminal; and a second input switch
coupled between the excitation source and the second excitation
terminal.
7. The circuit of claim 1, wherein the second set of input switches
comprises: a third input switch coupled between the excitation
source and the first sense terminal; and a fourth input switch
coupled between the excitation source and the second sense
terminal.
8. The circuit of claim 1, wherein the first set of output switches
comprises: a first output switch and a second output switch coupled
between the first sense terminal and the sense circuit; and a third
output switch and a fourth output switch coupled between the second
sense terminal and the sense circuit.
9. The circuit of claim 1, wherein the second set of output
switches comprises: a fifth output switch and a sixth output switch
coupled between the first excitation terminal and the sense
circuit; and a seventh output switch and an eighth output switch
coupled between the second excitation terminal and the sense
circuit.
10. The circuit of claim 1, wherein the sense circuit is configured
to measure the body impedance when the first input switch, the
second input switch, the first output switch and the fourth output
switch are closed.
11. The circuit of claim 1, wherein the sense circuit is configured
to measure: the first input electrode impedance when the first
input switch, the second input switch, the second output switch and
the fifth output switch are closed; and the second input electrode
impedance when the first input switch, the second input switch, the
third output switch and the eighth output switch are closed.
12. The circuit of claim 1, wherein the sense circuit is configured
to measure: the first output electrode impedance when the third
input switch, the fourth input switch, the first output switch and
the sixth output switch are closed; and the second output electrode
impedance when the third input switch, the fourth input switch, the
fourth output switch and the seventh output switch are closed.
13. A method comprising: measuring a body impedance; measuring at
least one electrode impedance of a plurality of electrode
impedances; generating an indication signal when at least one
electrode impedance of the plurality of electrode impedances is
above a defined threshold; and determining an accurate value of the
body impedance when each electrode impedance of the plurality of
electrode impedances is below the defined threshold, wherein the
accurate value of the body impedance is determined from the body
impedance and the plurality of electrode impedances.
14. The method of claim 13, wherein measuring the body impedance
further comprises closing a first input switch, a second input
switch, a first output switch and a third output switch.
15. The method of claim 13, wherein measuring at least one
electrode impedance further comprises: closing the first input
switch, the second input switch, a second output switch and a fifth
output switch, to measure a first input electrode impedance;
closing the first input switch, the second input switch, a fourth
output switch and a seventh output switch, to measure a second
input electrode impedance; closing a third input switch, a fourth
input switch, the first output switch and a sixth output switch, to
measure a first output electrode impedance; and closing the third
input switch, the fourth input switch, the third output switch and
an eighth output switch, to measure a second output electrode
impedance.
16. The method of claim 13, wherein determining the accurate value
of the body impedance further comprises using the body impedance,
the first input electrode impedance, the second input electrode
impedance, the first output electrode impedance and the second
output electrode impedance to determine the accurate value of the
body impedance, and each of the first input electrode impedance,
the second input electrode impedance, the first output electrode
impedance and the second output electrode impedance is below the
defined threshold.
17. The method of claim 13 further comprising generating a current
signal by an excitation source coupled between the first input
switch and the second input switch, wherein the excitation source
is coupled between the third input switch and the fourth input
switch.
18. The method of claim 13, wherein the body impedance coupled
between the first input electrode impedance and the second input
electrode impedance.
19. A computing device comprising: a processing unit; a memory
module coupled to the processing unit; and a impedance measurement
circuit coupled to the processing unit and the memory module, the
impedance measurement circuit comprising: an excitation source
coupled between a first set of input switches; an impedance network
coupled between the first set of input switches and a first set of
output switches, the impedance network having a body impedance and
a plurality of electrode impedances; and a sense circuit coupled to
the first set of output switches, the sense circuit configured to
measure the body impedance and at least one electrode impedance of
the plurality of electrode impedances.
20. The computing device of claim 19 further comprises a plurality
of electrodes, the plurality of electrodes includes a first
excitation electrode, a second excitation electrode, a first sense
electrode and a second sense electrode.
21. The computing device of claim 19, wherein the plurality of
electrode impedances comprises: a first input electrode impedance
coupled to a first excitation terminal, the first input electrode
impedance is corresponding to the first excitation electrode; a
second input electrode impedance coupled to a second excitation
terminal, the second input electrode impedance is corresponding to
the second excitation electrode, wherein the body impedance is
coupled between the first input electrode impedance and the second
input electrode impedance a first output electrode impedance
coupled to a first sense terminal, the first output electrode
impedance is corresponding to the first sense electrode; and a
second output electrode impedance coupled to a second sense
terminal, the second output electrode impedance is corresponding to
the second sense electrode.
22. The computing device of claim 19, wherein the sense circuit is
configured to: generate an indication signal when at least one
electrode impedance of the plurality of electrode impedances is
above a defined threshold; and determine an accurate value of the
body impedance when each electrode impedance of the plurality of
electrode impedances is below the defined threshold, and wherein
the sense circuit is configured to determine the accurate value of
the body impedance from the body impedance and the plurality of
electrode impedances.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority from India provisional
patent application No. 1926/CHE/2014 filed on Apr. 11, 2014 which
is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure is generally related to an impedance
measurement circuit, and more particularly to measuring electrode
impedance in the impedance measurement circuit.
BACKGROUND
[0003] In biomedical engineering, bio-impedance is the response of
a living organism to externally applied electric current.
Bio-impedance or body impedance is a measure of the opposition to
the flow of that electric current through the tissues, the opposite
of the electrical conductivity. The measurement of the body
impedance of humans and animals has proved useful as a non-invasive
method for measuring blood flow and body composition.
[0004] One method of measuring the body impedance is using
electrodes. A fixed excitation current (either AC or DC) is
injected in a human body through a pair of excitation electrodes. A
pair of sense electrodes is coupled to the human body. A sense
circuit measures a voltage difference across the sense electrodes.
The voltage difference corresponds to the impedance of the human
body.
[0005] An impedance associated with each electrode of the pair of
excitation electrodes and the pair of sense electrodes, affects the
accuracy of the measured body impedance. Traditional devices does
not take into consideration the high range of impedance associated
with the electrodes, because these devices provide large electrodes
which allow a large area of contact between the electrode and the
human body. However, modern consumer devices like cell phones need
to take into consideration the impedance associated with the
electrodes.
[0006] Existing solutions compensate for such high range of
electrode impedance by compromising on the sense circuit. In one
existing solution, the excitation current is reduced significantly
to compensate for the high range of impedance of the electrodes.
However, a reduction in excitation current also reduces the voltage
difference generated across the sense electrodes. This leads to
inaccuracies in the measurement of the body impedance.
SUMMARY
[0007] According to an aspect of the disclosure, a circuit is
disclosed. The circuit includes an excitation source coupled
between a first set of input switches. An impedance network is
coupled between the first set of input switches and a first set of
output switches. The impedance network includes a body impedance
and a plurality of electrode impedances. A sense circuit is coupled
to the first set of output switches. The sense circuit measures the
body impedance and at least one electrode impedance of the
plurality of electrode impedances.
BRIEF DESCRIPTION OF THE VIEWS OF DRAWINGS
[0008] FIG. 1 is a block diagram of an impedance measurement
circuit, in which various embodiments can be implemented;
[0009] FIG. 2 is a schematic of an impedance measurement
circuit;
[0010] FIG. 3 is a schematic of a circuit, according to an
embodiment;
[0011] FIG. 4 illustrates a method of impedance measurement,
according to an embodiment; and
[0012] FIG. 5 illustrates a computing device, according to an
embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0013] FIG. 1 is a block diagram of an impedance measurement
circuit 100, in which various embodiments can be implemented. The
impedance measurement circuit 100 is coupled to a human body 102.
The impedance measurement circuit 100 includes an excitation source
110. The excitation source 110 is coupled between a pair of
excitation electrodes 104 and 106. The excitation electrodes 104
and 106 are coupled to the human body 102. A pair of sense
electrodes 114 and 116 is also coupled to the human body 102. A
sense circuit 120 is coupled between the pair of sense electrodes
114 and 116.
[0014] The operation of the impedance measurement circuit 100
illustrated in FIG. 1 is explained now. The excitation source 110
generates an AC or a DC signal. In one example, the excitation
source 110 generates a high frequency AC current which is injected
in the human body 102 through the pair of excitation electrodes 104
and 106. The AC current causes a voltage difference between the
pair of sense electrodes 114 and 116. The sense circuit 120
measures this voltage difference. This voltage difference is
related to the resistivity of the human body 102 between the pair
of sense electrodes 114 and 116.
[0015] An impedance of the human body 102 is defined as the ratio
of the voltage difference between the pair of sense electrodes 114
and 116 and the AC current that is injected in the human body 102.
However, a number of factors affect the accuracy of the measured
impedance of the human body. These factors include, but not limited
to, connectivity of the pair of excitation electrodes 104 and 106
with the human body 102, and connectivity of the pair of sense
electrodes 114 and 116 with the human body 102.
[0016] The impedance between the electrode and the human body 102
could be much higher than the impedance of the human body. As a
result, it becomes difficult to determine if the readings by the
impedance measurement circuit 100 are accurate. Also, it is
difficult to determine the cause of error in the impedance
measurement circuit 100.
[0017] FIG. 2 is a schematic of an impedance measurement circuit
200. The impedance measurement circuit 200 is a schematic of
impedance measurement circuit 100, illustrated in FIG. 1. The
impedance measurement circuit 200 includes an excitation source 210
similar to the excitation source 110.
[0018] The excitation source 210 is coupled between a first
excitation terminal E1 204 and a second excitation terminal E2 206.
The first excitation terminal E1 204 corresponds to the excitation
electrode 104, and the second excitation terminal E2 206
corresponds to the excitation electrode 106. An impedance
associated with the excitation electrode 104 is represented by a
first input electrode impedance RE1 224, and an impedance
associated with the excitation electrode 106 is represented by a
second input electrode impedance RE2 226.
[0019] An impedance associated with the human body 102 is
represented as a body impedance RBODY 202. A sense circuit 220 is
coupled between a first sense terminal S1 214 and a second sense
terminal S2 216. The first sense terminal S1 214 corresponds to the
sense electrode 114, and the second sense terminal S2 216
corresponds to the sense electrode 116.
[0020] An impedance associated with the sense electrode 114 is
represented as a first output electrode impedance RE3 234, and an
impedance associated with the sense electrode 116 is represented as
a second output electrode impedance RE4 236. The first output
electrode impedance RE3 234 is coupled to the first input electrode
impedance RE1 224, the body impedance RBODY 202 and the first sense
terminal S1 214.
[0021] The second output electrode impedance RE4 236 is coupled to
the second input electrode impedance RE2 226, the body impedance
RBODY 202 and the second sense terminal S2 216.
[0022] The operation of the impedance measurement circuit 200
illustrated in FIG. 2 is explained now. The excitation source 210
generates and AC or a DC signal. In one example, the excitation
source 210 generates a high frequency AC current. The AC current is
injected in the human body through the pair of excitation
electrodes. The AC current traverses from the first excitation
terminal E1 204 to the second excitation terminal E2 206 through
the body impedance RBODY 202.
[0023] A voltage difference is created between the first sense
terminal S1 214 and the second sense terminal S2 216. The sense
circuit 220 measures this voltage difference. The voltage
difference provided a measure of the body impedance RBODY 202. The
body impedance RBODY 202 is a resistivity of the human body 102
between the first sense terminal S1 214 and the second sense
terminal S2 216.
[0024] The body impedance RBODY 202 is defined as the ratio of the
voltage difference between the first sense terminal S1 214 and the
second sense terminal S2 216, and the AC current that is generated
by the excitation source 210. However, a number of factors affect
the accuracy of the measured body impedance RBODY 202. These
factors include, but not limited to, connectivity of the pair of
excitation electrodes with the human body and connectivity of the
pair of sense electrodes with the human body.
[0025] Whenever an electrode is not in proper contact with the
human body, it results in increase in the magnitude of the
electrode impedance. For example, when the excitation electrode 104
is not in proper contact with the human body 102, it results in
increase in magnitude of the first input electrode impedance RE1
224. This results in inaccurate measurement of the body impedance
RBODY 202 by the sense circuit 220.
[0026] FIG. 3 is a schematic of a circuit 300, according to an
embodiment. The circuit 300, in one example, in an impedance
measurement circuit. The circuit 300 includes an excitation source
310, an impedance network 330 and a sense circuit 320. The
excitation source 310 is coupled between a first set of input
switches, which include a first input switch SI1 308 and a second
input switch SI2 312.
[0027] The impedance network 330 is coupled between the first set
of input switches and a first set of output switches. The first set
of output switches includes a first output switch SO1 342, a second
output switch SO2 344, a third output switch SO3 346 and a fourth
output switch SO4 348. The sense circuit 320 is coupled to the
first set of output switches.
[0028] A second set of input switches includes a third input switch
SI3 318 and a fourth input switch SI4 322. The second set of input
switches is coupled in parallel to the first set of input switches.
The excitation source 310 is coupled between the second set of
input switches i.e. the excitation source is coupled between the
third input switch SI3 318 and the fourth input switch SI4 322.
[0029] A second set of output switches includes a fifth output
switch SO5 352, a sixth output switch SO6 354, a seventh output
switch SO7 356 and an eighth output switch SO8 358. The second set
of output switches is coupled between the impedance network 330 and
the sense circuit 320. The impedance network 330 includes a body
impedance RBODY 302 and a plurality of electrode impedances. The
plurality of electrode impedance includes a first input electrode
impedance RE1 324, a second input electrode impedance RE2 326, a
first output electrode impedance RE3 334 and a second output
electrode impedance RE4 336.
[0030] The first input electrode impedance RE1 324 is coupled to a
first excitation terminal E1 304. The second input electrode
impedance RE2 326 is coupled to a second excitation terminal E2
306. The body impedance RBODY 302 is coupled between the first
input electrode impedance RE1 334 and the second input electrode
impedance RE2 326. The first output electrode impedance RE3 334 is
coupled to a first sense terminal S1 314, and the second output
electrode impedance RE4 336 is coupled to a second sense terminal
S2 316.
[0031] The first excitation terminal E1 304 corresponds to a first
excitation electrode (similar to the excitation electrode 104), and
the second excitation terminal E2 306 corresponds to a second
excitation electrode (similar to the excitation electrode 106). An
impedance associated with the first excitation electrode is
represented by the first input electrode impedance RE1 324, and an
impedance associated with the second excitation electrode is
represented by a second input electrode impedance RE2 326.
[0032] An impedance associated with the human body 102 is
represented as a body impedance RBODY 302. The first sense terminal
S1 314 corresponds to a first sense electrode (similar to the sense
electrode 114), and the second sense terminal S2 316 corresponds to
a second sense electrode (similar to the sense electrode 116). An
impedance associated with the first sense electrode is represented
as the first output electrode impedance RE3 334, and an impedance
associated with the second sense electrode is represented as the
second output electrode impedance RE4 336.
[0033] The first input switch SI1 308 is coupled between the
excitation source 310 and the first excitation terminal E1 304. The
second input switch SI2 312 is coupled between the excitation
source 310 and the second excitation terminal E2 306. The third
input switch SI3 318 is coupled between the excitation source 310
and the first sense terminal S1 314. The fourth input switch SI4
322 is coupled between the excitation source and the second sense
terminal S2 316.
[0034] The first output switch SO1 342 and the second output switch
SO2 344 are coupled between the first sense terminal S1 314 and the
sense circuit 320. The third output switch SO3 346 and the fourth
output switch SO4 348 are coupled between the second sense terminal
S2 316 and the sense circuit 320. The fifth output switch SO5 352
and the sixth output switch SO6 354 are coupled between the first
excitation terminal E1 304 and the sense circuit 320.
[0035] The seventh output switch SO7 356 and the eighth output
switch SO8 358 are coupled between the second excitation terminal
E2 306 and the sense circuit 320. In one version, the circuit 300
is part of a medical diagnostic device. In another version, the
circuit 300 is integrated in a consumer electronic device such as,
but not limited to, a mobile, a PDA (personal digital assistant),
and a smartphone. In yet another version, the circuit 300 is part
of a device used in industrial application. The circuit 300 may
include one or more additional components known to those skilled in
the relevant art and are not discussed here for simplicity of the
description.
[0036] The operation of the circuit 300 illustrated in FIG. 3 is
explained now. The excitation source 310 generates and AC or a DC
signal. In one example, the excitation source 310 generates a high
frequency AC current. The AC current is injected in the human body
through the pair of excitation electrodes. The AC current traverses
from the first excitation terminal E1 304 to the second excitation
terminal E2 306 through the body impedance RBODY 302.
[0037] The sense circuit 320 measures the body impedance RBODY 302,
and at least one electrode impedance of the plurality of electrode
impedances. The sense circuit 320 measures the body impedance RBODY
302 when the first input switch SI1 308, the second input switch
SI2 312, the first output switch SO1 342 and the fourth output
switch SO4 348 are closed.
[0038] The sense circuit 320 measures the first input electrode
impedance RE1 324 when the first input switch SI1 308, the second
input switch SI2 312, the second output switch SO2 344 and the
fifth output switch SO5 352 are closed. The sense circuit 320
measures the second input electrode impedance RE2 326 when the
first input switch SI1 308, the second input switch SI2 312, the
third output switch SO3 346 and the eighth output switch SO8 358
are closed.
[0039] The sense circuit 320 measures the first output electrode
impedance RE3 334 when the third input switch SI3 318, the fourth
input switch SI4 322, the first output switch SO1 342 and the sixth
output switch SO6 354 are closed. The sense circuit 320 also
measures the second output electrode impedance RE4 336 when the
third input switch SI3 318, the fourth input switch SI4 322, the
fourth output switch SO4 348 and the seventh output switch SO7 356
are closed.
[0040] A various combinations of the switches closed, and a
corresponding impedance measured by the sense circuit 320 is
illustrated in Table 1.
TABLE-US-00001 TABLE 1 Switches Closed Impedance Measured SI1, SI2,
SO1, SO4 RBODY SI1, SI2, SO5, SO8 RBODY + RE1 + RE2 SI3, SI4, SO5,
SO8 RBODY SI3, SI4, SO1, SO4 RBODY + RE3 + RE4 SI1, SI2, SO5, SO4
RBODY + RE1 SI1, SI2, SO1, SO8 RBODY + RE2 SI3, SI4, SO1, SO8 RBODY
+ RE3 SI3, SI4, SO5, SO4 RBODY + RE4 SI1, SI2, SO5, SO2 RE1 SI1,
SI2, SO3, SO8 RE2 SI3, SI4, SO1, SO6 RE3 SI3, SI4, SO7, SO4 RE4
[0041] The sense circuit 320 generates an indication signal when at
least one electrode impedance of the plurality of electrode
impedances is above a defined threshold. For example, when the
impedance of first input electrode impedance RE1 324 is above the
defined threshold, the sense circuit 320 generates the indication
signal. In one example, the defined threshold is provided by a
user. In another example, the defined threshold is a maximum
impedance of a human body.
[0042] In one version, when the circuit 300 is part of a medical
diagnostic device, the indication signal is used by a user to
understand that at least one electrode of the plurality of
electrodes is not making proper contact with the human body. In the
above example, the indication signal would signify that the first
excitation electrode (whose impedance is represented as RE1 324) is
not making proper contact with the human body.
[0043] The sense circuit 320 determines an accurate value of the
body impedance RBODY 302 when each electrode impedance of the
plurality of electrode impedances is below the defined threshold.
The sense circuit 320 determines the accurate value of the body
impedance RBODY 302 from the measured body impedance RBODY 302 and
the plurality of electrode impedances.
[0044] Thus, when each of the first input electrode impedance RE1
324, the second input electrode impedance RE2 326, the first output
electrode impedance RE3 334 and the second output electrode
impedance RE4 336 are below the defined threshold, the sense
circuit 320 determines the accurate value of the body impedance
RBODY 302. The sense circuit 320 determines the accurate value of
the body impedance RBODY 302 using the measured body impedance
RBODY 302, the first input electrode impedance RE1 324, the second
input electrode impedance RE2 326, the first output electrode
impedance RE3 334 and the second output electrode impedance RE4
336.
[0045] The accurate value of the body impedance RBODY 302 is more
precise than the body impedance RBODY 302 measured by the sense
circuit 320. The accurate value of the body impedance RBODY 302 is
a more precise measurement of the impedance of the human body by
the sense circuit 320. Thus, the circuit 300 provides a technique
to measure various impedances in the impedance network 330, which
is used by the sense circuit 320 for determination of the accurate
value of the body impedance RBODY 302 which is more precise than
the measured body impedance RBODY 302. By measuring various
impedances in the impedance network 330, the circuit 300 provides a
reliable and accurate means for measuring the impedance of the
body.
[0046] FIG. 4 illustrates a method 400 of impedance measurement,
according to an embodiment. At step 402, a body impedance is
measured. An excitation source generates and AC or a DC current
signal. In one example, the excitation source generates a high
frequency AC current. The AC current is injected in the human body
through the pair of excitation electrodes.
[0047] In circuit 300 the body impedance RBODY 302 is measured when
the first input switch SI1 308, the second input switch SI2 312,
the first output switch SO1 342 and the fourth output switch SO4
348 are closed. In one version, a body impedance represents an
impedance of a human body. At step 404, at least one electrode
impedance of the plurality of electrode impedances is measured.
[0048] In circuit 300, at least one of the first input electrode
impedance RE1 324, the second input electrode impedance RE2 326,
the first output electrode impedance RE3 334 and the second output
electrode impedance RE4 336 is measured. An indication signal is
generated when at least one electrode impedance of the plurality of
electrode impedances is above a defined threshold, at step 406.
[0049] In one example, the defined threshold is provided by a user.
In another example, the defined threshold is a maximum impedance of
the human body. The indication signal signifies that at least one
electrode of the plurality of electrodes is not making proper
contact with the human body. At step 408, an accurate value of the
body impedance is determined when each electrode impedance of the
plurality of electrode impedances is below the defined threshold.
The accurate value of the body impedance is determined from the
measured body impedance and the plurality of electrode
impedances.
[0050] For example, in circuit 300, when each of the first input
electrode impedance RE1 324, the second input electrode impedance
RE2 326, the first output electrode impedance RE3 334 and the
second output electrode impedance RE4 336 is below the defined
threshold, the sense circuit 320 determines the accurate value of
the body impedance RBODY 302. The sense circuit 320 determines the
accurate value of the body impedance RBODY 302 using the measured
body impedance RBODY 302, the first input electrode impedance RE1
324, the second input electrode impedance RE2 326, the first output
electrode impedance RE3 334 and the second output electrode
impedance RE4 336.
[0051] The accurate value of the body impedance RBODY 302 is more
precise than the measured body impedance RBODY 302. The accurate
value of the body impedance RBODY 302 is a more precise measurement
of the impedance of the human body. The method 400 provides a
reliable technique to measure impedance of the human body. The
measurement of electrode impedances provides a unique way of fault
detection, and a user is provided the indication signal for making
better contact with the electrodes.
[0052] FIG. 5 illustrates a computing device 500, according to an
embodiment. The computing device 500 is, or is incorporated into, a
mobile communication device, such as a mobile phone, a personal
digital assistant, a transceiver, a personal computer, or any other
type of electronic system. The computing device 500 may include one
or more additional components known to those skilled in the
relevant art and are not discussed here for simplicity of the
description.
[0053] In some embodiments, the computing device 500 comprises a
megacell or a system-on-chip (SoC) which includes a processing unit
512 such as a CPU (Central Processing Unit), a memory module 514
(e.g., random access memory (RAM)) and a tester 510. The processing
unit 512 can be, for example, a CISC-type (Complex Instruction Set
Computer) CPU, RISC-type CPU (Reduced Instruction Set Computer), or
a digital signal processor (DSP).
[0054] The memory module 514 (which can be memory such as RAM,
flash memory, or disk storage) stores one or more software
applications 530 (e.g., embedded applications) that, when executed
by the processing unit 512, performs any suitable function
associated with the computing device 500. The tester 510 comprises
logic that supports testing and debugging of the computing device
500 executing the software applications 530.
[0055] For example, the tester 510 can be used to emulate a
defective or unavailable component(s) of the computing device 500
to allow verification of how the component(s), were it actually
present on the computing device 500, would perform in various
situations (e.g., how the component(s) would interact with the
software applications 530). In this way, the software applications
530 can be debugged in an environment which resembles
post-production operation.
[0056] The processing unit 512 typically comprises memory and logic
which store information frequently accessed from the memory module
514. A camera 518 is coupled to the processing unit 512. The
computing device 500 includes an impedance measurement circuit 516.
The impedance measurement circuit 516 is coupled to the processing
unit 512 and the memory module 514. The impedance measurement
circuit 516 is coupled to an electrode chip 520.
[0057] The electrode chip 520 includes a first excitation electrode
522, a second excitation electrode 524, a first sense electrode 526
and a second sense electrode 528. In one version, the electrode
chip 520 is integrated in the computing device 500. In another
version, the first excitation electrode 522, the second excitation
electrode 524, the first sense electrode 526 and the second sense
electrode 528 are positioned in the computing device 500
appropriately based on the application of the computing device 500.
In yet another version, the electrode chip is separate from the
computing device 500, and may communicate with the computing device
500 by a wired/wireless medium. In a different version, the
electrode chip 520 includes a plurality of electrodes. The
operation of the impedance measurement circuit 516 is similar the
operation of the circuit 300 illustrated in FIG. 3.
[0058] The first excitation terminal E1 304 in circuit 300
corresponds to the first excitation electrode 522, and the second
excitation terminal E2 306 corresponds to the second excitation
electrode 524. An impedance associated with the first excitation
electrode 522 is represented by the first input electrode impedance
RE1 324, and an impedance associated with the second excitation
electrode 524 is represented by a second input electrode impedance
RE2 326.
[0059] The first sense terminal S1 314 corresponds to the first
sense electrode 526, and the second sense terminal S2 316
corresponds to the second sense electrode 528. An impedance
associated with the first sense electrode 526 is represented as the
first output electrode impedance RE3 334, and an impedance
associated with the second sense electrode 528 is represented as
the second output electrode impedance RE4 336.
[0060] The impedance measurement circuit 516 includes a sense
circuit similar to the sense circuit 320. The sense circuit
generates an indication signal when at least one electrode
impedance of the plurality of electrode impedances is above a
defined threshold. For example, when the first input electrode
impedance RE1 324 is above the defined threshold, the sense circuit
320 generates the indication signal.
[0061] In one version, when the computing device 500 is part of a
medical diagnostic device, the indication signal is used by a user
to understand that at least one electrode of the plurality of
electrodes is not making proper contact with the human body. In the
above example, the indication signal would signify that the first
excitation electrode 522 is not making proper contact with the
human body. In another example, the impedance measurement circuit
516 is used for fault detection, in which case the indication
signal is used by a user to understand that the combination of
fingers used for touching electrodes is not correct. For example,
in one case, when the user is touching both the first excitation
electrode 522, and the second excitation electrode 524 with fingers
of same hand, the sense circuit generates an indication signal.
[0062] The sense circuit determines an accurate value of the body
impedance when each electrode impedance of the plurality of
electrode impedances is below the defined threshold. The sense
circuit 320 determines the accurate value of the body impedance
RBODY 302 from the body impedance RBODY 302 and the plurality of
electrode impedances.
[0063] The accurate value of the body impedance is a more precise
measurement of the impedance of the human body by the sense
circuit. Thus, the impedance measurement circuit 516 provides a
reliable technique for measuring body impedance.
[0064] The foregoing description sets forth numerous specific
details to convey a thorough understanding of the invention.
However, it will be apparent to one skilled in the art that the
invention may be practiced without these specific details.
Well-known features are sometimes not described in detail in order
to avoid obscuring the invention. Other variations and embodiments
are possible in light of above teachings, and it is thus intended
that the scope of invention not be limited by this Detailed
Description, but only by the following Claims.
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