Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2000-06-16
2003-04-29
Le, N. (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S071500, C324S762010, C257S414000
Reexamination Certificate
active
06556025
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to signal measurement or detection, and more particularly to a method of generating output corresponding to changes in signal input received from a sensor and to an on-chip measurement circuit using a charge coupled readout scheme.
BACKGROUND OF THE INVENTION
Capacitive readout circuits can generally be classified into three basic categories, namely inductor-capacitor (LC) resonators, capacitive bridge circuits and switched capacitor circuits on an integrated circuit (IC) chip. Prior art LC resonators are difficult to implement with very low value capacitors because they must operate at extremely high frequencies, and require very high quality factors (Q) in order to resolve small frequency shifts.
Conventional capacitive bridge circuits require a perfect match of the sensor capacitance to that of the reference capacitor, which is difficult to achieve, especially with mass fabrication. The switched capacitor approach is very useful for implementation of on-chip capacitive sensors, but is complex in terms of circuit design and signal processing requirements.
In light of the limitations of conventional capacitance readout circuits, there is a need for high-resolution capacitance measurement circuits that are capable of measuring very small changes in capacitance and which can be incorporated into an integrated circuit design.
In addition to capacitance readout circuits, a need exists in other applications for high-resolution measurement circuits that are capable of detecting very small changes in the output signals generated by sensors. It is therefore an object of the present invention to provide a novel method of generating output corresponding to changes in signal input received from a sensor and a novel on-chip measurement circuit using a charge coupled readout scheme.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a method of generating output corresponding to a change in signal input received from a sensor comprising the steps of:
providing a direct current (DC) or low frequency (AC) bias to said sensor; and
coupling a floating gate of a semiconductor device to said sensor so that changes in signal input received from said sensor modulate charge at said gate, said semiconductor device converting modulated charge into an output signal proportional to the change in the sensor input.
The floating-gate semiconductor device is responsive to changes in sensor input in the sub-atto range and converts the modulated charge at the gate into a current. The current appears as a voltage across terminals of the semiconductor device that is proportional to the change in the sensor input. In a preferred embodiment, the floating-gate semiconductor device is a metal oxide semiconductor field effect transistor (MOSFET). The gate of the MOSFET is coupled directly to the sensor. The voltage appears across the drain and source terminals of the MOSFET.
According to another aspect of the present invention there is provided a method of measuring changes in signal level-output of an integrated circuit sensor comprising the steps of:
providing a direct current (DC) or low frequency (AC) bias to said sensor; and
placing a floating gate semiconductor device on-chip and with the floating gate of said semiconductor device being directly coupled to said sensor so that changes in signal level output of said sensor modulate charge at said gate, said semiconductor device converting modulated charge at said gate into output signals proportional to the changes in said signal level output.
According to still yet another aspect of the present invention there is provided an on-chip signal measurement method of generating output proportional to a change in signal level output of an integrated circuit sensor using a floating gate semiconductor device, said method comprising the steps of:
DC or low frequency AC biasing said sensor;
applying the signal level output of said integrated circuit sensor to said floating gate so that a change in the signal level output modulates gate charge;
converting the modulated gate charge into an output signal proportional to the change in said signal level output.
According to still yet another aspect of the present invention there is provided a method of measuring changes in the signal level output of a sensor, on-chip, comprising the steps of
DC or low frequency AC biasing said sensor; and
using an on-chip charge coupled scheme to detect changes in the signal level output of said sensor and to generate output signals corresponding thereto.
According to still yet another aspect of the present invention there is provided a measurement circuit for use with an integrated circuit sensor, said measurement circuit comprising:
a DC or low frequency AC source to bias said sensor; and
an on-chip floating gate semiconductor device, said semiconductor device including a drain node, a source node and a gate node, said gate node being coupled directly to said sensor so that a change in the signal level output of said sensor modulates charge at said gate node, said semiconductor device converting the change in the charge at said gate node into a drain-source current that appears as a drain-source voltage proportional to the change in said signal level output.
The present invention provides advantages in that the measurement method and circuit increases resolution sensitivity significantly (by three orders of magnitude) as compared to conventional low-level measurement techniques (i.e. measurement of changes in sensor signal level output down to the sub-atto (10
−18
) range). Also, the present invention provides advantages due to the fact that a DC or low frequency AC bias is used and as a result, the design of the measurement circuit is simple. This, of course, avoids the high fabrication costs and the increased circuit topography requirements associated with conventional low-level measurement devices, which use high frequency AC signal sources.
The combined ability to measure changes in sensor signal level output at the sub-atto range and to utilize a DC or low frequency AC source allows the present measurement method and circuit to extend signal measurement applications to new levels of sensitivity as well as to introduce low level signal measurement to new fields of application not possible with prior art measurement devices. The measurement method and circuit of the present invention can be used with virtually any type of sensor and has applications in capacitance based sensors, such as microphones, sensitive pressure sensors, micro-mechanical actuators that require feedback, and in accelerometers (e.g. for automobile air bags, anti-lock brakes, etc.) to name but a few. The measurement method and circuit of the present invention is also particularly useful in integrated chip design and fabrication for in-situ characterization of interface capacitance or parasitic capacitance associated with individual components that comprise integrated circuits.
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Lu Yong
Manku Tajinder
Nathan Arokia
Connolly Bove & Lodge & Hutz LLP
Deb Anjan K.
Le N.
University of Waterloo
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