LOW NOISE AMPLIFIERS WITH FEEDBACK FOR NANOPORE APPLICATIONS
Disclosed herein are devices, systems, and methods that can improve the SNR of nanopore measurements by mitigating the effect of parasitic capacitance between the sense electrode and the counter electrode. In some embodiments, a feedback circuit is used to inject a charge into the sense electrode to at least partially cancel the parasitic capacitance between the sense electrode and the counter electrode. In some embodiments, bootstrapping of a signal from the amplifier output or from the sense electrode is used to inject a charge on the counter electrode to substantially cancel the parasitic capacitance.
1 . A system for detecting molecules, the system comprising:
an array comprising a plurality of nanopore units, each of the plurality of nanopore units comprising a nanopore, a sense electrode, and a counter electrode;
drive circuitry coupled to the array of nanopore units;
an amplifier;
a multiplexer coupled to the array of nanopore units and to an input of the amplifier;
a feedback circuit coupled to an output of the amplifier and to the input of the amplifier; and
control logic coupled to the feedback circuit and to the multiplexer and configured to:
control the multiplexer to select a first nanopore unit of the plurality of nanopore units for reading, and
configure the feedback circuit to provide a first amount of feedback for the first nanopore unit.
2 . The system recited in claim 1 , wherein the first amount of feedback is:
(a) dependent on an identity of the first nanopore unit, and/or
(b) applicable to the first nanopore unit and at least one other nanopore unit in the array.
3 . The system recited in claim 1 , further comprising memory coupled to the control logic, and wherein the control logic is further configured to:
retrieve information from the memory, the information associated with a prior configuration of the feedback circuit.
4 . The system recited in claim 3 , wherein the prior configuration of the feedback circuit was a custom configuration for the first nanopore unit.
5 . The system recited in claim 1 , further comprising tuning logic coupled to the feedback circuit, wherein the tuning logic is configured to:
adjust at least one parameter of the feedback circuit to increase or decrease the first amount of feedback.
6 . The system recited in claim 1 , further comprising tuning logic coupled to the feedback circuit, wherein the tuning logic is configured to:
increase the first amount of feedback,
detect an onset of instability in an amplifier output signal, and
decrease the first amount of feedback in response to the detected onset of instability, thereby settling the first amount of feedback at a tuned amount of feedback.
7 . The system recited in claim 6 , further comprising memory coupled to the tuning logic, and wherein the tuning logic is further configured to:
store configuration information in the memory, the configuration information associated with the tuned amount of feedback.
8 . The system recited in claim 7 , wherein the control logic is coupled to the memory, and wherein the control logic is further configured to retrieve the configuration information from the memory and to configure the feedback circuit to provide the tuned amount of feedback for the first nanopore unit.
9 . The system recited in claim 1 , wherein the control logic is further configured to:
control the multiplexer to select a second nanopore unit of the plurality of nanopore units, and
configure the feedback circuit to provide a second amount of feedback for the second nanopore unit.
10 . The system recited in claim 9 , wherein the second amount of feedback differs from the first amount of feedback.
11 . The system recited in claim 9 , further comprising memory coupled to the control logic, and wherein the control logic is further configured to:
retrieve first information from the memory, the first information associated with a prior configuration of the feedback circuit for the first nanopore unit, and
retrieve second information from the memory, the second information associated with a prior configuration of the feedback circuit for the second nanopore unit.
12 . The system recited in claim 9 , further comprising tuning logic coupled to the feedback circuit, wherein the tuning logic is configured to:
adjust at least one parameter of the feedback circuit to increase or decrease the first amount of feedback, and/or
adjust the at least one parameter of the feedback circuit to increase or decrease the second amount of feedback.
13 . The system recited in claim 9 , further comprising tuning logic coupled to the feedback circuit, wherein the tuning logic is configured to adjust at least one parameter of the feedback circuit to:
(a) provide a same amount of feedback for the first nanopore unit and the second nanopore unit, and/or
(b) provide a customized amount of feedback depending on an identity of a nanopore unit selected by the multiplexer.
14 . The system recited in claim 9 , wherein the first amount of feedback is substantially equal to the second amount of feedback.
15 . A method of reducing noise in a nanopore signal at an input of an amplifier, the method comprising:
applying a voltage to a nanopore to produce the nanopore signal at the input of the amplifier;
configuring an aspect of a feedback circuit coupled to and situated between an output of the amplifier and the input of the amplifier;
detecting a characteristic of an amplifier output signal;
adjusting the aspect of the feedback circuit in response to the detected characteristic of the amplifier output signal; and
the feedback circuit injecting a feedback signal at the input of the amplifier.
16 . The method of claim 15 , wherein the aspect of the feedback circuit is a capacitance.
17 . The method of claim 15 , wherein the characteristic of the amplifier output signal comprises at least one of:
(a) a signal-to-noise ratio;
(b) an error rate associated with an error correcting code protecting data represented by the nanopore signal;
(c) a downstream process or component determining the characteristic of the amplifier output signal;
(d) a stability;
(e) an amount of oscillation.
18 . The method of claim 15 , wherein detecting the characteristic of the amplifier output signal comprises processing a digitized version of the amplifier output signal.
19 . The method of claim 15 , wherein the characteristic of the amplifier output signal comprises a stability, and wherein adjusting the aspect of the feedback circuit in response to the detected characteristic of the amplifier output signal comprises:
adjusting the aspect of the feedback circuit to increase an amount of feedback provided at the input of the amplifier;
detecting an onset of instability in the amplifier output signal after adjusting the aspect of the feedback circuit to increase the amount of feedback provided at the input of the amplifier; and
in response to detecting the onset of instability in the amplifier output signal, adjusting the aspect of the feedback circuit to decrease the amount of feedback provided at the input of the amplifier.
20 . The method of claim 19 , wherein detecting the onset of instability in the amplifier output signal comprises detecting oscillations in the amplifier output signal.
21 . The method of claim 15 , further comprising:
determining an optimized aspect of the feedback circuit by iteratively (a) detecting the characteristic of the amplifier output signal, and (b) adjusting the aspect of the feedback circuit in response to the detected characteristic of the amplifier output signal.
22 . The method of claim 21 , further comprising:
storing information identifying the optimized aspect of the feedback circuit in memory.
23 . The method of claim 22 , further comprising:
retrieving the information identifying the optimized aspect of the feedback circuit from the memory,
and wherein configuring the aspect of the feedback circuit comprises configuring the aspect in accordance with the information identifying the optimized aspect of the feedback circuit.