1. NOISE EFFECT IN INSTRUMENT AMPLIFIER APPLICATIONS AHMAD FIRDAUS BIN ABDUL AZIZ (2110384) MOHD SHASZWAN AZEEM BIN ISMAIL(2110389) A SPECIFIC INSTRUMENTATION AMPLIFIER WITH A GUARD OUTPUT

2. What is noise?? An electronic signal that is a mixture of many random frequencies at many amplitudes that gets added to a radio or information signal as it is transmitted from one place to another. Examples of noise ▫When you turn on any radio receiver and tune it to some position between stations, the hiss or static that you hear in the speaker is noise ▫Noise also shows up on a black and white TV screen as snow or on colour screen as confetti

3. TYPES OF NOISE External noise Atmospheric Noise Extraterrestrial Noise Industrial Noise Internal Noise Thermal Noise Shot noise Semiconductor Noise

4. NOISE EFFECT IN INSTRUMENT APPLICATION Various types of tranduser are used to sense temperature, strain, pressure, and other parameters in many types of applications. Instrument amplifiers are generally used to process the small voltages produces by a tranduser and in noisy industrial environment. Noise in the form of common mode signals picked up from external sources can be minimized, but not totally eliminated, by using coaxial cable in which the different signal wires are surounded by a metal mesh sheating called a shield.

5. NOISE EFFECT IN INSTRUMENT APPLICATION In an electrically noisy environment any common-mode signal that are induced on the signal lines are rejected because both inputs to the amplifier have the same common-mode signal. However, when a shielded cable used, there are stray capacitance distributed along its length between each signal line and the shield. The difference in these stray capacitance, particularly at higher frequencies.

6. NOISE EFFECT IN INSTRUMENT APPLICATION Degradation of common-mode rejection in a shielded cable connection due to unwanted phase shifts.

7. NOISE EFFECT IN INSTRUMENT APPLICATION SHIELD GUARD  Guarding is a technique to reduce the effect of noise on the common-mode operation of an instrument amplifier by connecting the common-mode voltage to the shield of a coaxial cable.  The common-mode signal is fed back to the shield by a voltage- follower stage,  The purpose is to eliminated voltage differences between the signal lines and the shield, virtually eliminating leakage current and cancelling the effects of the distributed capacitance so that the common-mode voltages are the same in both lines.

8. NOISE EFFECT IN INSTRUMENT APPLICATION SHIELD GUARD  The voltage-follower is a low-impendence source that drives the common-mode signal onto the shield to eliminate the voltage difference between the signal lines and the shield.  When the voltage between each signal line and the shield is zero, the leakage current are also zero and the capacitive reactance become infinity large. An infinitely large Xc implies a zero capacitance

9. A SPECIFIC INSTRUMENTATION AMPLIFIER WITH A GUARD OUTPUT Most instrumentation amplifiers can be configured externally to provide a shield guard driver. Certain IC amplifiers, however, provides an internally generated guard output that is intended for very critical environment.

10. A SPECIFIC INSTRUMENTATION AMPLIFIER WITH A GUARD OUTPUT Example ▫AD522 ▫A precision IC instrumentation amplifier designed for application requiring high accuracy under worst-case operating conditions and very small signal. ▫The pin labeled DATA GUARD is the shield-guard output.

11. REFERENCES Electronic devices conventional current version ninth edition Floyd Copyright© 2012 Pearson Education, Inc.,