Analog multiplexer

Figure 23.29. Analog multiplexer. From S. P. Perone and D, O. Jones,...

Multiplexii. It is sometimes necessary to sample more than one experimental waveform simultaneously during a single experiment. To accomplish this, an analog multiplexer can be used, the configurational and sampling considerations of which will be discussed here. 

The primary characteristic of an analog multiplexer is that it can accommodate multiple analog inputs, any one of which can be sampled through a single output channel. The selection of the input channel to be transmitted to the digitization hardware can be accomplished by a binary-coded command from the computer or by generating an appropriate external sequencing code. The critical characteristic is the time required to switch between input channels. With solid-state... 

The reader should recognize immediately that the analog multiplexer need not provide the slow step in an overall data-acquisition process. Indeed, the slower processes will be associated with the data-acquisition hardware and software that follow the analog multiplexer. Another point is that it is impossible for the multiplexer to sample independent waveforms in a truly simultaneous fashion. Some finite time-interval must exist between samplings of different channels. The manner in which this problem is handled will depend on the need for acquiring truly simultaneous data from the different channels. 

An EIT system needs an automatic ESM. An electrode switching module may be developed with analog multiplexers or any other automatic electronic switching devices, like relays. 

FIGURE 7.74 Programmable gain amplifier consisting of a dual 4-to-1 analog multiplexer and a difference amplifier. 

At low frequencies, the resistances of the switches used to create the analog multiplexers have no effect on the output voltage, but they may affect the results at higher frequencies if parasitic capacitances are not kept to low values. However, the properties of real or tangible op-amps (as opposed to ideal op-amps) will most likely impose tighter limits on the range of frequencies over which this circuit and any of the circuits in this section can be used. Furthermore, real op-amp characteristics will affect gain accuracies. In the next section, we discuss the characteristics of real op-amps and show how these characteristics can be modeled. 

Multifunction boards are commonly used to measure analog signals. It is done by the ADC, which converts the analog voltage level into a digital number that the computer can interpret. The analog multiplexer (MUX), the instrumentation amplifier, the sample-and-hold (S/H) circuitry, and the ADC comprise the analog input section of a multifunction board (see Fig. 18.26). 

Fig. 16 Modeling of crosstalk noise in A -channel analog multiplexer...

Similar to the buffers that drive the analog multiplexer presented before, the power consumption of the buffers to drive ADCs are also determined by the... 

The power consumed by the analog multiplexer was so small that it can be neglected here. Also, the power consumption of buffers and ADCs were respectively... 

Table 2 is the calculation result with various numbers of channels and ADCs. Here it can be seen that when it comes to power consumption, a one ADC per one channel system is the best, which is a very natural result because it does not need buffers to drive the analog multiplexer. 

Each preamplifier and buffer draws 2 and 20.3 p.A respectively, to drive the analog multiplexer when it is turned on by the sequential turn-on control signals, leading to an average current of 2.54 p.A. The second amplifier draws 40.6 p,A to drive 10-pF input sampling capacitance of the SAR ADC. 

The analog multiplexer block (64 to 16 lines). In our case there are only 57 analog signals to be elaborated. 

---