Signal slew rates

There is no upper limit for the possibilities of an intelligent process monitoring. From a simple analysis of the maximum values of a pressure signal to the analysis of signal slew rates for specific applications, a whole range of monitoring functions is possible and practical. 

Fig. 7.12 Ratio of the signal resulting from ionization of m = 2 states (upper curve), and ionization of m = 0 states (lower curve) to the total ionization signal as a function of the slew rate from low to intermediate fields following excitation of the 34dj/2 state via the 3pifl state with o polarization (from ref. 16).

Note however, that the amplifier gain must be dynamically changed depending on signal amplitude, which leads to discontinuities. Kriz also points out the slew rate problems in the track and hold. His solution was to use a DC feedback loop with an analog integrator. 

FKsl.IRi 3-9 Response of an operalionat amplifier to a rapid step change in input voltage. The slope of Ihe changing portion of the output signal is Uie slew rate, and Ihe time required for the output to change from i0% lo 90% of the total change is the rise trme. 

The Gunn oscillator frequency-lock became progressively more unstable as its slewing rate increased, whether caused by rapid frequency stepping or by the application of FM. We found ourselves limited in practice to a stepping time of 50-100 ms and an FM deviation of 10 MHz at a rate of 1 kHz. This was considered reasonably satisfactory in that a complete scan could be completed in a few seconds and that our signal detection rate 2 kHz was close to the frequency at which manufacturers, e.g. Millitech, specified their detector performance. The same FM rate was used whether our detector was a Schottky barrier mixer diode or the helium-cooled bolometer. 

The slope of the signal is also surveyed by the sensing circuit and is determined by the slew rate (the time rate of change in voltage). A slew rate that is too flat or too steep may be eliminated by the bandpass filter. On average, the slew rate measured at implant should be between 0.75 and 2.50 V/s. 

FIGURE 11.6 A conceptual depiction of the bandpass filter, demonstrating the typical filtering of unwanted signals by discriminating between those with slew rates that are too low and/or too high. 

One of the most costly computations in timing analysis is propagating the slew rate of a signal through the circuit. However, changes in slew rate typically do not propagate... 

Some portions of the signal may not have adequate amplitude and slew rate to be sensed because of the complex nature of the lEGM. Typically, the portion... 

Fig. 2.7 Slew rate, or the change in voltage divided by the change in time of an intracardiac signal.

Full power bandwidth The frequency at which a sinusoidal signal having large amplitude begins to become distorted at the output of an op-amp due to the slew rate limitation. Full power bandwidth, ftipB in rad/s, is related to SR by )fb = SR/Vomax where Vomax is the peak value of output voltage. 

The Slew rate in the real world is a measure of an amplifier s ability to follow the input signal. Higher numbers are better, with 100 resulting in no change. 

This means that lowering the slew rate simulates the distortion plug-in not keeping up with changes in amplitude in the signal. The result is a characteristic type of noise in the output signal. 

An exponential approximation of slewing is now considered. Assume that the valve can move from its zero position to its 100% position in Tioo seconds, at a constant rate, when a step input signal is applied at t = 0 seconds. Assume that an equivalent exponential lag term responds to the same step input over the same period of Tioo seconds. Figure 2.18 shows the two responses referred to a common base of time. A good measure of fit can be made by choosing the time constant Tfa such that the area represented by the lower part (A) equals that represented by the upper area (B). This is determined by equating these two areas. The areas are found by integration. Area (A) is found by... 

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