Delta modulated baseline restoration for photon counting computed tomography
One embodiment is a baseline restoration (“BLR”) circuit for a photo-counting computed tomography (“PCCT”) signal chain, the BLR circuit comprising a comparator for comparing a shaper voltage output from a shaper component of the PCCT signal chain with a baseline voltage, the comparator outputting a single bit indicative of whether the shaper voltage is above or below the baseline voltage; a low pass filter connected to filter a voltage signal output from the comparator; and a transconductor connected to receive a filtered voltage signal output from the low pass filter, convert the filtered voltage signal to a current signal, and feed the current signal back to an input of the PCCT signal chain.
1 . A baseline restoration (“BLR”) circuit for a photon-counting computed tomography (“PCCT”) signal chain, the BLR circuit comprising:
an input comparator for comparing a shaper voltage output from a shaper component of the PCCT signal chain with a baseline voltage, the input comparator outputting a single bit indicative of whether the shaper voltage is above or below the baseline voltage; and
a low pass filter connected to filter a voltage signal output from the input comparator.
2 . The BLR circuit of claim 1 , further comprising a transconductor connected to receive a filtered voltage signal output from the low pass filter, convert the filtered voltage signal to a current signal, and feed the current signal back to an input of the PCCT signal chain.
3 . The BLR circuit of claim 1 , comprising a delta modulator circuit for providing nonlinear BLR.
4 . The BLR circuit of claim 3 , wherein the low pass filter comprises an integrator of the delta modulator circuit.
5 . The BLR circuit of claim 1 , further comprising a feedback loop that functions as a delta modulator.
6 . The BLR circuit of claim 1 , wherein the BLR circuit is clocked.
7 . The BLR circuit of claim 1 , wherein chopper stabilization is applied to null out an offset of the input comparator.
8 . The BLR circuit of claim 1 , wherein an auto-zero technique is applied to null out an offset of the input comparator.
9 . The BLR circuit of claim 1 , wherein the BLR circuit is clocked and chopper stabilization is applied to null out an offset of the input comparator.
10 . The BLR circuit of claim 1 , wherein the BLR circuit is clocked and an auto-zero technique is applied to null out an offset of the input comparator.
11 . The BLR circuit of claim 1 , wherein the low pass filter is in a non-feedback configuration.
12 . A method for implementing non-linear baseline restoration (“BLR”), the method comprising:
comparing a shaper voltage output from a shaper component of a photon-counting computed tomography (PCCT) signal chain with a baseline voltage to produce a comparator voltage indicative of whether the shaper voltage is above or below the baseline voltage at a given time;
filtering the comparator voltage; and
converting the filtered voltage signal to a current signal.
13 . The method of claim 12 , further comprising feeding the current signal back to an input of the PCCT signal chain.
14 . The method of claim 13 , wherein the comparing, filtering, converting, and feeding is performed by a delta-modulation circuit.
15 . The method of claim 12 , further comprising clocking the comparing and filtering.
16 . The method of claim 12 , further comprising applying chopper stabilization to null out an offset of an input comparator of the PCCT signal chain.
17 . The method of claim 12 , further comprising applying an auto-zero technique to null out an offset of an input comparator of the PCCT signal chain.
18 . The method of claim 12 , further comprising:
clocking the comparing and filtering; and
applying chopper stabilization to null out an offset of an input comparator of the PCCT signal chain.
19 . The method of claim 12 , wherein the filtering is performed using a low-pass filter.
20 . The method of claim 19 , further comprising applying a low-duty-cycle clock signal to the low-pass filter to increase a value of a time constant.