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The backplane environment presents a serious challenge to signaling rates above 5Gb/s. Previous 10Gb/s transceivers [1] are not designed for this harsh environment. In the raw single bit response of Fig. 4.6.1, a single 200ps pulse undergoes serious loss and dispersion and initiates reflections that may be a significant percentage of an equalized eye. Figure 4.6.1 (inset) shows a zoom-in of the reflections plotted on a scale equivalent to a single 4-PAM equalized eye. The total usable amplitude after equalization is slightly smaller than 3d which is the distance between the peak sample point and the next sample point of the raw pulse response. While the use of multiple signaling levels and transmit equalization help minimize the effects of dispersion [2,3], transmit-only equalization is an expensive way to combat the effect of reflections which are more destructive to multi-level signaling. Decision feedback-based receive equalization (DFE) is effective when dealing with configuration dependent reflections. The design of both transmit and receive equalizers and clock recovery circuits are described for operation in this type of backplane environment.Since dispersion is a function of many properties in backplanes, flexibility in the transmit equalizer, both in number of taps and their settings is highly desirable. One completely flexible approach involves the use of a digital filter and DAC [4], while the simplest approach is two-tap pre-emphasis [5]. Any technique must be evaluated for both additional insertion loss as well as for power and complexity.The five-tap merged differential transmitter/equalizer shown in Fig. 4.6.2 leverages the fact that the total transmitted current is limited to less than the sum of the maximum taps to reduce pad parasitics. It achieves this by using large segments that can be individually allocated to any tap position. The transmit equalizer is partitioned into a shared section and a dedicated section. The shared section consists of 7 large sub-drivers, each driving 16i current, where each shared sub-driver can select from any of the 5 equalization tap streams A -E. The dedicated portion consists of five binary weighted drivers, one for each equalization tap, and each capable of driving up to 15i current. This combination of shared and dedicated drivers allows each equalization tap to have the same current range, 127i, and resolution, 1i, of a non-equalizing 7b transmitter with only 50% additional parasitic overhead. Comparatively, a 5-tap transmitter/equalizer with the same range and resolution implemented by replicating the primary driver has a 400% parasitic overhead. A pure digital filter and DAC implementation requires a FIR filter running at the symbol rate and consumes more than twice the power.For receive equalization, the linearity and high bandwidth of the transmission line environment were leveraged by adding and subtracting currents directly at the input pads. The receive equalizer is equivalent to a 1/5th scaled transmit equalizer. High-latency reflections are effective...

An instrument to measure the excited-state lifetimes of phosphorescent materials in real time is described. This apparatus uses pulsed and frequency-doubled Nd:YAG solid-state laser for excitation, sampler for data acquisition, and frequency domain methods for data fitting. The instrument amplifies the ac components of the detector output and band limits the signal to 25 kHz. The fundamental frequency of the excitation is then set to obtain a desired number of harmonics. This band limited signal is sampled and averaged over few thousand cycles in the time domain. The frequency domain representation of the data is obtained by employing fast Fourier transform algorithms. The phase delay and the modulation ratio of each sampled harmonic is then computed. Ten to a hundred values of the phase and modulations are averaged before computing the sensor lifetime. The instrument is capable of measuring precise and accurate excited-state lifetimes from subpicowatt luminescent signals in 100 μm optical fibers. To monitor oxygen for biomedical applications the response time of the system is decreased by collecting only 8 or 16 harmonics. A least-squares fit yields the lifetimes of single exponentials. A component of zero lifetime is introduced to account for the backscatter excitation. The phosphorescence lifetimes measured reproducibly to three parts in a thousand are used to monitor oxygen. Oxygen concentrations are computed employing empirical polynomials. The system drift is less than 1% over 100 h of continuous operation. This instrument is used to measure oxygen concentrations in vitro and in vivo with 2 s update times and 90 s full response times. Examples of measurements in saline solutions and in dogs are presented.