US 6,630,669 B1 · Correlated modulation imaging (CMI)

Abstract

In the present invention of Correlated Modulation Imaging (CMI), the weak optical image signal (and therefore the signal current) is modulated, and the signal integration direction is correlated to the modulation. Therefore, the dark and/or background current, which are not modulated, are cancelled, while the signal current is integrated. As a result, the total integration time of the signal of each pixel is increased, and its signal to noise ratio and dynamic range are improved. Besides, the CMI noise spectrum peaks at the modulation frequency, and therefore, the detector's 1/f and other low frequency noises can be suppressed. In the present invention, the method and theory of CMI, as well as the means and steps for the realization of CMI, are explicitly developed. Two versions of CMOS devices (CMI unit pre-amplifier version 1 and 3), with their circuitry design and testing data are presented as the critical component for correlated modulation imaging. A prototype chip of the CMI circuitries has been fabricated by the MOSIS 0.5-micron foundry. SPICE circuitry simulation has demonstrated the functioning of CMI unit pre-amplifier version 1 and 3 as designed. Experimental work has demonstrated the functioning of CMI unit pre-amplifier version 1 as designed, as well as the key features of CMI—increase of integration time, and improvement of signal to noise ratio and dynamic range.

Claims2

Dependent claims

A circuit design of CMI unit pre-amplifier using one operational amplifier to perform the function of correlated modulation imaging (CMI), which is composed of

a. a first stage S2 including an integrator (30), said integrator (30) comprising an operational amplifier (30), a feedback capacitor C (24), and a reset switch M5 (42), wherein the capacitor C (24) accumulates signal throughout multi-cycle integration, while the reset switch M5 enabled at beginning of integration with a narrow pulse, and reset after readout of the integrated signal;
and
b. a second stage S1 including a demodulator (29), said demodulator comprising a temporal integrator C1 (35) and three MOSFET switches M2, M3, and M4 being gates of integrator (35);
when M2 and M3 are off and M4 is on, an input current Iin (15) is integrated on C1 first;
at the end of the half period of integration, by turning off M4 followed by turning on M2 and M3, the charges stored on the right plate (35b) of C1, will be transferred to the left plate (24a) of C, while at the same time, C1 is reset;
assuming that the charges stored on said right plate (35b) are Q1, the change of output voltage Vo at node (27) after the transfer is ΔVo1=−Q1/C;
at the next phase or half period of integration, with said M3 and M4 off and M2 on, said input current Iin charges said C1 and C;
assuming at the end of this period of integration the charges accumulated on the right plate (35b) of C1 is Q2, the change of output voltage Vout at node (27) after the transfer is ΔVo2=Q2/C;
thus, the total change of output voltage Vout at node (27) after the two consecutive integrations is ΔVout=Qs/C and the function of the CMI method, integration of signal and cancellation of background, is fulfilled.

6 more elements

Dependencies are inferred from the claim text.

Correlated modulation imaging (CMI)

Life of this patent

Correlated modulation imaging (CMI)

Life of this patent

Abstract

Claims2