Scalp potential measuring method and apparatus
An apparatus for measuring scalp potential is disclosed, which comprises a plurality of sensors and a pre-amplifier coupled to these sensors. The sensors are adapted to measure a raw scalp potential measurement though a hair and air interface, and may be considered as a difference, reference or common measurement. The interface presents a high and variable source impedance coupling to the scalp. The pre-amplifier is adapted to have an input impedance significantly higher than that presented by the source interface, and receives the raw scalp potential measurement to produce a pre-amplified scalp potential measurement.
1. A method for processing scalp potential signals comprising receiving an input raw scalp potential signal from a plurality of sensors for defining a respective plurality of channels;
processing the input raw scalp potential signal using a plurality of pre-amplifiers thereby to provide a high input impedance, wherein each pre-amplifier includes:
(i) a wideband high impedance input and active biasing network, which presents an impedance of greater than 10 Peta-Ohms from 0.01 Hz to 400 Hz;
(ii) a high gain low noise operational amplifier, with an input impedance of 10 Tera Ohms; and
(iii) a feedback network for feeding back a first feedback signal interconnected to a conductive shield surrounding the input raw scalp potential signal, and a second feedback signal for actively biasing the input raw scalp potential signal;
selecting a measurement mode configuration wherein the measurement mode configuration is selected from the group consisting of:
a channel to reference-channel mode;
a channel to channel-average mode; and
a channel to channel differential mode;
biasing said processed input signal while maintaining high input impedance;
matching channel gain before differentially deriving a channel signal for each of the plurality of channels;
processing each channel signal using the selected measurement mode configuration thereby to provide a corresponding processed channel signal, wherein the processing of each channel signal includes:
suppressing radio frequency interference of each channel signal while maintaining gain and phase matching; and
suppressing common mode signal interference of each channel signal;
band pass filtering each said processed channel signal; and
digitizing each said processed channel signal thereby to provide a digital scalp potential measurement signal indicative of said scalp potential signals having been processed.
2. A method according to claim 1 wherein each pre-amplifier includes a high input impedance amplifier for amplifying said raw scalp potential signal, and wherein the method includes amplifying said raw scalp potential signal to produce a pre-amplified scalp potential measurement.
3. A method according to claim 2 wherein said input impedance provided by each pre-amplifier is higher with respect to the impedance associated with a source interface presented to each said sensor.
4. A method according to claim 3 wherein said source interface impedance is presented by at least one of a contact medium, scalp, and underlying tissues.
5. A method according to claim 2 , wherein said input impedance provided by each pre-amplifier is active and increased by the application of feedback.
6. A method according to claim 1 , wherein said high gain low noise operational amplifier is a rail-to-rail FET input operational amplifier.
7. An apparatus for processing scalp potential signals comprising:
a plurality of sensors for receiving an input raw scalp potential signal, wherein the plurality of sensors define a respective plurality of channels;
a plurality of pre-amplifier modules each including a pre-amplifier for processing the input raw scalp potential signal thereby to provide a high input impedance, wherein each pre-amplifier includes:
(ii) a wideband high impedance input and active biasing network, which presents an impedance of greater than 10 Peta-Ohms from 0.01 Hz to 400 Hz;
(iii) a high gain low noise operational amplifier, with an input impedance of 10 Tera Ohms; and
(iv) a feedback network for feeding back a first feedback signal interconnected to a conductive shield surrounding the input raw scalp potential signal, and for actively biasing the input raw scalp potential signal;
a channel interconnection module adapted to select a measurement mode from the group consisting of:
a channel to reference-channel mode;
a channel to channel-average mode; and
a channel to channel differential mode;
an interface module for:
biasing said processed input signal while maintaining high input impedance;
matching channel gain before differentially deriving a channel signal for each of the plurality of channels;
processing each channel signal using the selected measurement mode configuration thereby to provide a corresponding processed channel signal, wherein the processing of each channel signal includes:
suppressing radio frequency interference of each channel signal while maintaining gain and phase matching; and
suppressing common mode signal interference of each channel signal;
band pass filtering each said processed channel signal; and
an analog-to-digital converter module for digitizing each said processed channel signal thereby to provide a digital scalp potential measurement signal indicative of said scalp potential signals having been processed.
8. An apparatus according to claim 7 wherein each pre-amplifier includes a high input impedance amplifier for amplifying said raw scalp potential signal to produce a pre-amplified scalp potential measurement.
9. An apparatus according to claim 8 wherein said input impedance provided by each pre-amplifier is higher with respect to the impedance associated with a source interface presented to each said sensor.
10. An apparatus according to claim 7 , wherein said high gain low noise operational amplifier is a rail-to-rail FET input operational amplifier.