FET applications


Posted on Feb 6, 2014

FET has a very high input impedance (100 Mega ohm in case of JFETs and 104 to 109 Mega Ohm in case of MOSFETs), the major shortcomings of an ordinary transistor i. e. low input impedance with consequent of loading of signal source is eliminated in FET. Hence FET is an ideal device for use in almost every application in which transistors can be used


FET applications
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. FETs are widely used as input amplifiers in oscilloscopes, electronic voltmeters and other measuring and testing equipment because of their high input impedance. FETs are used as voltage-variable resistors (WRs) in operational amplifiers (op-amps) and tone controls etc, for mixer operation on FM and TV receivers and in logic circuits. 1. Low Noise Amplifier. Noise is an undesirable disturbance super-imposed on auseful signal. Noise interferes with the information contained in the signal; the greaterthe noise, the less the information. For instance, the noise in radio-receivers developscrackling and hissing which sometimes completely masks the voice or music. Similarly, the noise in TV receivers produces small white or black spots on the picture; a severe Every electronic device produces certain amount of noise but FET is a device which causes very little noise. This is especially important near the front-end of the receivers and other electronic equipment because the subsequent stages amplify front-end noise along with the signal. If FET is used at the front-end, we get less amplified noise (disturbance) at the final output. A buffer amplifier is a stage of amplification that isolates thepreceding stage from the following stage. Source follower (common drain) is. used as abuffer amplifier. Because of the high input impedance and low output impedance a FETacts an excellent buffer amplifier, as shown in figure. Owing to...




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