High-Speed Mixed-Signal Circuit Design
The speed of integrated circuits has improved as smaller amounts of charge are moved smaller distances in smaller transistors. This increase in speed has been used in a variety of applications: Computers have gotten more powerful through a combination of faster and more complex processors; Radios in devices as varied as self-setting clocks and cell phones have migrated from custom components to standard integrated circuits; And entirely new classes of instruments are possible because of this increased speed.
Our primary experience in high-speed mixed-signal circuit design has been driven by the study of time-domain fluorescence. Fluorophores are widely used in biology as labels. After excitation by light at one wavelength, fluorophores emit light at another wavelength. Traditionally, the excitation light is filtered out before measuring the emission light using spectral interference filters. Because the statistics of the time-domain emission of photons followed pulsed excitation is well defined for a given fluorophore, we developed a technique for filtering in the time domain. This technique can increase the number of fluorescence channels, decrease the cost of fluorescence instruments, or improve the accuracy of ratiometric fluorescence measurements in lossy environments. The challenge is that it requires measuring the fluorescence emission on a nanosecond time scale. To put that into perspective light only travels about a foot in one nanosecond. Our nanosecond pixel was presented in the TBCAS paper below.
C. Salthouse, R. Weissleder, and U. Mahmood "Development of a Time Domain Fluorimeter (TDF) for Fluorescent Lifetime Multiplexing Analysis" IEEE TBCAS, vol. 2, iss. 3, pp. 204-211, Sept. 2008