Methods and systems for readout of nanogap sensors

Abstract

Embodiments of the present disclosure relate to various methods and example systems for carrying out analog-to-digital conversion of data acquired by arrays of nanogap sensors. The nanogap sensors described herein may operate as molecular sensors to help identify chemical species through electrical measurements using at least a pair of electrodes separated by a nanogap. In general, the methods and systems proposed herein rely on digitizing the signal as the signal is being integrated, and then integrating the digitized results. With such methods, the higher sample rate used in the digitizer reduces the charge per quantization and, therefore, the size of sampling capacitors used. Consequently, sampling capacitors may be made factors of magnitude smaller, requiring less valuable space on a chip compared to sampling capacitors used in conventional nanogap sensor arrays.

1 - 20 . (canceled) 
     
     
         21 . A method of operating a system that includes an array of nanogap sensors configured to evaluate one or more fluid analytes, the method comprising:
 applying one or more signals to one or more selector transistors corresponding to a first nanogap sensor of the array to select the first nanogap sensor for readout; and   determining an oscillation frequency of a relaxation oscillator coupled to the first nanogap sensor, where the relaxation oscillator is configured to oscillate with the oscillation frequency indicative of a current generated by the first nanogap sensor.   
     
     
         22 . The method according to  claim 21 , further comprising:
 determining the current generated by the first nanogap sensor based on the determined oscillation frequency; and   determining presence and/or amount of at least one of the one or more fluid analytes based on the determined current.   
     
     
         23 . A multiplexer for selecting individual nanogap sensors from an array of nanogap sensors configured to evaluate one or more fluid analytes, the multiplexer comprising:
 pairs of transistors corresponding to individual nanogap sensors in a one-to-one correspondence,   wherein each pair of transistors includes a pass transistor and a dump transistor, and wherein, when an individual nanogap sensor is selected for readout:
 a pass transistor of a pair of transistors corresponding to the individual nanogap sensor is on, 
 a dump transistor of the pair of transistors corresponding to the individual nanogap sensor is off, 
 pass transistors of all other nanogap sensors of the array are off, and 
 dump transistors of all other nanogap sensors of the array are on. 
   
     
     
         24 . A system for readout of one or more nanogap sensors, the system comprising:
 an analog electrode to receive current from a plurality of sensors electrodes;   an integrator having a capacitor to integrate current from the analog electrode;   a comparator to compare the integrated current with a reference voltage;   a counter circuit which increase a count every time the integrator reaches the reference voltage in the comparator; and   a cancellation circuit to remove charge from the capacitor.   
     
     
         25 . The system according to  claim 24 , wherein the cancellation circuit removes the charge from the capacitor every time the count is increased. 
     
     
         26 . The system according to  claim 24 , wherein the counter circuit is configured to determine a number of counts during a predetermined time period. 
     
     
         27 . The system according to  claim 26 , wherein the number of counts during the predetermined period is a digital representation of the current from the plurality of sensors electrodes. 
     
     
         28 . The system according to  claim 24 , wherein the cancellation circuit comprises one or more cancellation capacitors. 
     
     
         29 . The system according to  claim 28 , wherein the cancellation circuit is in electrical communication with a cancellation reference voltage. 
     
     
         30 . The system according to  claim 24  further comprising a filtering circuit. 
     
     
         31 . The system according to  claim 30 , wherein the filtering circuit is configured to decimate the count. 
     
     
         32 . The system according to  claim 30 , wherein the filtering circuit is configured to smooth the count. 
     
     
         33 . The system according to  claim 30 , wherein the filtering circuit is configured to average the count over a second predetermined period of time. 
     
     
         34 . The system according to  claim 24  further comprising a multiplexor. 
     
     
         35 . The system according to  claim 34 , wherein the multiplexor is configured to multiplex the count with other data channels. 
     
     
         36 . The system according to  claim 30  further comprising a register configured to store the count. 
     
     
         37 . The system according to  claim 24 , wherein the current from the plurality of sensors electrodes are combined together to represent an average current from the plurality of sensors at the analog electrode. 
     
     
         38 . The system according to  claim 37  further comprising a current conveyer disposed in between the analog electrode and integrator. 
     
     
         39 . The system according to  claim 38 , wherein the current conveyer is a cascode. 
     
     
         40 . The system according to  claim 24 , wherein the plurality of sensors electrodes are in electrical communication with a plurality of nanogap sensors.