Apparatus and methods for removing a large-signal voltage offset from a biomedical signal
Apparatus and methods remove a voltage offset from an electrical signal, specifically a biomedical signal. A signal is received at a first operational amplifier and is amplified by a gain. An amplitude of the signal is monitored, by a first pair of diode stages coupled to an output of the first operational amplifier, for the voltage offset. The amplitude of the signal is then attenuated by the first pair of diode stages and a plurality of timing banks. The attenuating includes limiting charging, by the first pair of diode stages, of the plurality of timing banks and setting a time constant based on the charging. The attenuating removes the voltage offset persisting at a threshold for a duration of at least the time constant. Saturation of the signal is limited to a saturation recovery time while the saturated signal is gradually pulled into monitoring range over the saturation recovery time.
1. A method for processing an electrical signal having a large differential voltage offset, comprising:
receiving, at a differential input of a first operational amplifier in a circuit, the electrical signal;
amplifying, by the first operational amplifier in the circuit, the electrical signal by a gain;
limiting, by a first pair of diode stages in the circuit that are coupled to a differential output of the first operational amplifier, the electrical signal for the large differential voltage offset;
delaying, by a plurality of timing banks of the circuit, the electrical signal;
attenuating, by a second pair of diode stages in the circuit that are coupled to the plurality of timing banks, an amplitude of the electrical signal, thereby producing a differential signal; and
limiting, by the circuit, a saturation duration of the differential signal to less than a saturation recovery time.
2. The method of claim 1 , wherein the gain of the first operational amplifier is about 40.
3. The method of claim 1 , wherein the saturation recovery time is less than 100 milliseconds.
4. The method of claim 1 , wherein the attenuating further comprises:
pulling, by the second pair of diode stages, a positive input node voltage of the first operational amplifier down toward a common mode reference voltage and a negative input node voltage of the first operational amplifier up toward the common mode reference voltage; and
limiting, by the second pair of diode stages, the differential signal from the plurality of timing banks, wherein the positive input node voltage and the negative input node voltage are pulled into a monitoring range after about the saturation recovery time.
5. The method of claim 1 , wherein the limiting the electrical signal for the large differential voltage offset further comprises:
limiting charging, by the first pair of diode stages, of the plurality of timing banks in response to respective voltage outputs of a differential output of the first operational amplifier being less than a breakdown voltage of a diode in the first pair of diode stages.
6. The method of claim 1 , wherein the amplifying further comprises:
amplifying, by the first operational amplifier, the electrical signal by the gain in response to the large differential voltage offset being above an activation threshold for a duration of time at least as long as a time constant, wherein the activation threshold is 100 mV.
7. The method of claim 1 , further comprising:
disconnecting, by the second pair of diode stages, an output of the circuit to a system in response to the large differential voltage offset being below an activation threshold.
8. The method of claim 1 , wherein the delaying further comprises:
charging a resistor-capacitor network of the plurality of timing banks; and
setting, by the plurality of timing banks, a time constant based on the charging of the resistor-capacitor network of the plurality of timing banks.
9. The method of claim 8 , wherein the time constant is 2 milliseconds to 10 milliseconds.