Ultra-low-power front end for beyond-the-rails voltage sensing
A system may include a passive floating attenuator configured to receive an analog physical quantity and attenuate the analog physical quantity to a floating attenuated signal defined by voltage nodes other than the voltage nodes of the analog physical quantity, an anti-aliasing filter configured to filter the floating attenuated signal to generate a filtered attenuated signal, and a switched-capacitor sampling circuit comprising a plurality of switches configured to sample the filtered attenuated signal.
1 . A system comprising:
a passive floating attenuator configured to receive an analog physical quantity and attenuate the analog physical quantity to a floating attenuated signal defined by voltage nodes other than the voltage nodes of the analog physical quantity;
an anti-aliasing filter configured to filter the floating attenuated signal to generate a filtered attenuated signal; and
a switched-capacitor sampling circuit comprising a plurality of switches configured to sample the filtered attenuated signal.
2 . The system of claim 1 , wherein the passive floating attenuator comprises a resistive divider.
3 . The system of claim 1 , wherein the switched-capacitor sampling circuit comprises a common-mode insensitive sampling circuit insensitive to a common mode of the filtered attenuated signal.
4 . The system of claim 1 , further comprising a bootstrap generation network electrically coupled to the plurality of switches and configured to:
generate a bootstrap sampling clock for controlling the plurality of switches; and
generate a floating supply voltage for the bootstrap sampling clock based on the filtered attenuated signal.
5 . The system of claim 4 , further comprising a unity gain buffer configured to buffer the filtered attenuated signal used for generating the bootstrap sampling clock in order to isolate an output of the anti-aliasing filter from the bootstrap generation network.
6 . The system of claim 5 wherein the unity gain buffer is powered from a floating supply that is derived from and tracks a highest-voltage beyond-the-rails component of the analog physical quantity.
7 . The system of claim 1 , wherein the analog physical quantity is a voltage.
8 . A method comprising:
attenuating, with a passive floating attenuator, an analog physical quantity to a floating attenuated signal defined by voltage nodes other than the voltage nodes of the analog physical quantity;
filtering, with an anti-aliasing filter, the floating attenuated signal to generate a filtered attenuated signal; and
sampling the filtered attenuated signal with a switched-capacitor sampling circuit comprising a plurality of switches.
9 . The method of claim 8 , wherein the passive floating attenuator comprises a resistive divider.
10 . The method of claim 8 , wherein the switched-capacitor sampling circuit comprises a common-mode insensitive sampling circuit insensitive to a common mode of the filtered attenuated signal.
11 . The method of claim 8 , further comprising:
generating, with a bootstrap generation network electrically coupled to the plurality of switches, a bootstrap sampling clock for controlling the plurality of switches; and
generating, with the bootstrap generation network, a floating supply voltage for the bootstrap sampling clock based on the filtered attenuated signal.
12 . The method of claim 11 , further comprising buffering, with a unity gain buffer, the filtered attenuated signal used for generating the bootstrap sampling clock in order to isolate an output of the anti-aliasing filter from the bootstrap generation network.
13 . The method of claim 12 , wherein the unity gain buffer is powered from a floating supply that is derived from and tracks a highest-voltage beyond-the-rails component of the analog physical quantity.
14 . The method of claim 8 , wherein the analog physical quantity is a voltage.