High-Z input amplifiers are particularly useful when interfaced with sensors that have relatively high output impedance. Such multichannel systems usually interface these sensors with the signal chain through multiplexers. You can use the circuit shown in Figure 4a with an amplifier to interface with each sensor and connect to the inputs of a multiplexer. An alternate circuit, shown in Figure 4b, uses a single fast-settling amplifier at the output of a multiplexer that is directly connected to the sensors.
Figure 4c shows the output voltage and input differential voltage when applying an 8V step at the noninverting input of the OPA configured as a unity-gain buffer in Figure 4b.
Figure 4: A multichannel sensor front end with multiple slow-settling amplifiers a ; using a single OPA with fast settling b ; large-signal transient response using the OPA c. Because of the fast input transient, the amplifier is slew-limited and the inputs cease to track each other a maximum V IN,Diff of 7V is seen Figure 4c until the output reaches its final value and the negative feedback loop is closed.
For standard amplifiers with a 0. The OPA has in-built input clamps that allow the application of as much as 7V of V IN,Diff , with no need for external resistors and no damage to the device or a shift in performance specifications. Such an input-stage architecture coupled, with its fast settling performance, makes the OPA a good fit for multichannel sensor multiplexed systems.
In a majority of these applications, high-speed amplifiers may be driving successive approximation register SAR or pipeline ADCs. Because the ADCs have input capacitors switching in and out during the sampling intervals, you must use an amplifier to prevent from input loading when driving these converters. For fast sampling rates, the ADC input needs to settle fast to within 0.
The OPA settles to within 0. Because of its large slew rate and fast settling performance, you could use the OPA amplifier to digitize multiple lower-frequency signals at its input. Hence, JFET-input amplifiers, like the OPA , offer a variety of benefits in different high-speed applications discussed above due to their high-Z inputs, superior distortion performance, fast settling and wide-supply range.
Make sure to look at the family of high-Z input high-speed amplifiers from TI to select the one that best suits your application requirements. Site Search User. Share Contact author Subscribe by email More Cancel. Similar topics. Both g, and g, are dynamic parameters defined at and around the Q-point and their accurate measurement is the subject of this article. It is the maximum current in the tolerance range of drain-source voltages, VDS, that can be achieved.
What is the main advantage of FET which makes it more useful in industrial applications? Explanation: Because of its small size, the IC chips can be made even smaller which reduces the wear and tear. The N-channel JFET's channel is doped with donor impurities meaning that the flow of current through the channel is negative hence the term N-channel in the form of electrons.
Field effect transistors FETs work on a pricipal that uses the field produced by the gate in a way that makes the channel conduct more or less. The FET was named such because the of how the static field , as apposed to current, plays a central role in the operation of the device.
The gate -to-source voltage is used to control the depletion region of the JFET. At first, is set to zero ; the depletion region on both sides is formed. The input current is always zero as the gate -to-source junction is never forward biased.
Hence, the current is effectively for a JFET transistor. This means that they practically draw no current and therefore do not load down the power circuit that's feeding it. The JFET can be fabricated in small size area. It is a majority charge carrier device, hence it has less noise.
It is a low power consumption device. It can be fabricated in small size area. It occupies less space in circuits due to its smaller size. A FET is a three terminal device, having the characteristics of high input impedance and less noise, the Gate to Source junction of the FET is always reverse biased. In amplifier application, the FET is always used in the region beyond the pinch-off.
Obviously dual gate FETs have two gates and both need to be incorporated into the circuit symbol. The bipolar junction transistor is a current controlled device.
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