Hearing device with a means for receiver current estimation and a method of estimating a receiver current for a hearing device
A hearing device with a unit for estimating the current consumed by the receiver of the hearing device. The hearing device includes a signal input unit for converting an input signal picked up by the signal input unit into a digital audio signal, a signal processing unit for processing the digital audio signal, a digital-to-analog converter for converting a processed audio signal from the signal processing unit, a power amplifier for amplifying a converted audio signal from the digital-to-analog converter, a receiver for generating sound according to an amplified audio signal from the power amplifier, and a battery for powering the hearing device. A receiver current estimation unit has a filter for filtering a receiver current indicative signal derived from the processed audio signal, the filter having a frequency response dependent on an impedance of the receiver. A method is provided for estimating a receiver current for a hearing device.
1. A hearing device comprising a signal input means ( 1 ) for converting an input signal picked up by the signal input means ( 1 ) into a digital audio signal, a signal processing unit ( 2 ) for processing the digital audio signal, a digital-to-analog converter ( 3 ) for converting a processed audio signal from the signal processing unit ( 2 ), a power amplifier ( 4 ) for amplifying a converted audio signal from the digital-to-analog converter ( 3 ), a receiver ( 5 ) for generating sound according to an amplified audio signal from the power amplifier ( 4 ), and a battery ( 6 ) for powering the hearing device, characterised in that the hearing device further comprises a receiver current estimation unit ( 7 ) comprising a filter ( 8 ) for filtering a receiver current indicative signal derived from the processed audio signal, the filter ( 8 ) having a frequency response H(f) which is dependent on an impedance Z(f) of the receiver ( 5 ) and an amplitude response |H(f)| of the filter ( 8 ) is approximately dependent on the impedance Z(f) of the receiver ( 5 ) as given by the relation: |H(f)|≈√{square root over (|Z(f)| −1 )}.
2. The hearing device of claim 1 , wherein the filter ( 8 ) is an eighth or higher order filter.
3. The hearing device of claim 2 , wherein the filter ( 8 ) comprises at least four biquads.
4. The hearing device of claim 1 , wherein the receiver current estimation unit ( 7 ) further comprises an analog-to-digital converter ( 9 ) for measuring a supply voltage V BatPA of the power amplifier ( 4 ).
5. The hearing device of claim 4 , wherein the receiver current estimation unit ( 7 ) further comprises an averaging unit ( 10 ) for averaging the output signal from the analog-to-digital converter ( 9 ) and a multiplier ( 11 ) for multiplying the output signal from the averaging unit ( 10 ) with a signal dependent on an output of the filter ( 8 ).
6. The hearing device of claim 1 , wherein the receiver current estimation unit ( 7 ) further comprises a squaring unit ( 12 ) for squaring the output signal of the filter ( 8 ), and preferably also a second averaging unit ( 10 ′) for averaging the output signal from the squaring unit ( 12 ).
7. The hearing device of claim 1 , wherein the receiver current estimation unit ( 7 ) is adapted to determine an estimate of the receiver current I est (f) based on the following formula:
I
est
(
f
)
=
V
BatPA
·
1
N
∑
n
=
0
N
H
(
f
)
·
s
(
n
)
2
,
wherein V BatPA is the supply voltage of the power amplifier ( 4 ), preferably an average value of the supply voltage of the power amplifier ( 4 ), s(n) are discrete-time samples of the receiver current indicative signal, and N is the number of discrete-time samples processed to determine a value of the estimate of the receiver current I est (f).
8. The hearing device of claim 1 , wherein the receiver current indicative signal is a down-sampled version of the processed audio signal extracted from within the digital-to-analog converter ( 3 ).
9. A hearing device comprising a signal input means ( 1 ) for converting an input signal picked up by the signal input means ( 1 ) into a digital audio signal, a signal processing unit ( 2 ) for processing the digital audio signal, a digital-to-analog converter ( 3 ) for converting a processed audio signal from the signal processing unit ( 2 ), a power amplifier ( 4 ) for amplifying a converted audio signal from the digital-to-analog converter ( 3 ), a receiver ( 5 ) for generating sound according to an amplified audio signal from the power amplifier ( 4 ), and a battery ( 6 ) for powering the hearing device, characterised in that the hearing device further comprises a receiver current estimation unit ( 7 ) comprising a filter ( 8 ) for filtering a receiver current indicative signal derived from the processed audio signal, the filter ( 8 ) having a frequency response H(f) which is dependent on an impedance Z(f) of the receiver ( 5 ), wherein coefficients c(f) of the filter ( 8 ) are approximately dependent on the impedance Z(f) of the receiver ( 5 ) as given by the relation: c(f)≈|Z(f)| −1 .
10. A method of estimating a receiver current for a hearing device powered by a battery ( 6 ), comprising the steps of:
converting an input signal picked up by a signal input means ( 1 ) into a digital audio signal;
processing the digital audio signal by a signal processing unit ( 2 );
converting a processed audio signal from the signal processing unit ( 2 ) by a digital-to-analog converter ( 3 );
amplifying a converted audio signal from the digital-to-analog converter ( 3 ) by a power amplifier ( 4 );
generating sound according to an amplified audio signal from the power amplifier ( 4 ) by a receiver ( 5 );
characterised in
filtering by a filter ( 8 ) a receiver current indicative signal derived from the processed audio signal, the filter ( 8 ) having an amplitude response |H(f)| which is approximately dependent on the impedance Z(f) of the receiver ( 5 ) as given by the relation: |H(f)|≈√{square root over (|Z(f)| −1 )}.
11. The method of claim 10 , further comprising the steps of:
determining a value of a supply voltage V BatPA of the power amplifier ( 4 ), preferably an average value of the supply voltage V BatPA of the power amplifier ( 4 ); and
multiplying a signal dependent on an output of the filter ( 8 ) with the value of the supply voltage V BatPA of the power amplifier ( 4 ), preferably the average value of the supply voltage V BatPA of the power amplifier ( 4 ).
12. The method of claim 11 , wherein the steps are performed in order to evaluate the following formula:
I
est
(
f
)
=
V
BatPA
·
1
N
∑
n
=
0
N
H
(
f
)
·
s
(
n
)
2
,
wherein s(n) are discrete-time samples of the receiver current indicative signal, and N is the number of discrete-time samples processed to determine a value of an estimate of the receiver current I est (f).
13. The method of claim 10 , wherein coefficients c(f) of the filter ( 8 ) are determined by the steps of:
applying a signal with a certain peak value ŝ and a certain frequency f to the receiver ( 5 );
measuring a receiver current I meas (ŝ, f);
repeating the previous two steps for different peak values ŝ i at multiple frequencies f j ; and
solving a linear least-squares problem on the following set of equations:
[
I
meas
(
s
^
min
,
f
min
)
…
I
meas
(
s
^
min
,
f
max
)
⋮
⋱
⋮
I
meas
(
s
^
max
,
f
min
)
…
I
meas
(
s
^
max
,
f
max
)
]
︸
I
meas
=
1
2
·
V
BatPA
·
[
s
^
min
2
⋮
s
^
max
2
]
︸
A
·
[
c
(
f
min
)
…
c
(
f
max
)
]
︸
c
,
or
equivalently
c
=
I
meas
A
,
wherein c is a vector of filter coefficients c(f), which are to be determined, I meas is a matrix of measured receiver currents and A is a matrix of amplitude values.
14. The method of claim 13 , wherein the filter ( 8 ) is a recursive filter, the method further comprising determining coefficients of the recursive filter based on a Yule-Walker method.
15. The method of claim 10 , wherein coefficients c(f) of the filter ( 8 ) are determined by the steps of:
measuring the impedance Z(f) of the receiver ( 5 ) at multiple frequencies f j ; and
computing the coefficients c(f) of the filter ( 8 ) based on the relation: c(f)≈|Z(f)| −1 .
16. The method of claim 10 , wherein frequency characteristics of the filter ( 8 ) are determined individually for the specific receiver ( 5 ) utilised in the hearing device prior to regular operation of the hearing device by a user of the hearing device.