# why input impedance should be high

Calculation of input resistance, or, more correctly, input impedance, was presented in Chapter 2. 6.11 are interchanged is that of an exponential or antilog (inverse log) amplifier. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. The noninverting op amp has the highest input impedance, that of the op amp itself. why should input impedance be high in op-amps etc and output impedance be low??? Why input impedance should be high for an amplifier? The most sensitive setting on a typical oscilloscope is 1 mV/division, and the standard oscilloscope input resistance is 1 MΩ. If the inputs are ν1 = 1 mV and ν2 = 0.9 mV, calculate the output voltages for the two amplifiers and show the effect that a higher CMRR has. Importance of the Impedances. 6.20 we have iL = νs/R1. what's the principle involved?? By way of illustration, hybrid-π parameters for a typical microwave BJT are shown in Tables 12.2 and 12.3 . Am I correct in understanding this? We use the word “generally” here because there is a special case where this rule does not apply. See Figure 4.38. How long will the footprints on the moon last? D.I. I.e., so the measurement is not affected and is correct? You have available a temperature-to-voltage transducer which generates a voltage of 5 V at 160°C and an alarm which activates at −15 V and is off for larger voltages. With the box set to zero resistance, and the input signal set at 200 μV at 10 Hz, the gain of the amplifier is adjusted to give a deflection of about 2 cm. 6.23. The inverse of gm has the dimensions of resistance, that is, 1/gm = re. The load gets the high voltage which comes from the source output. It varies with both input frequency and operating temperature. Dennis L. Feucht, in Handbook of Analog Circuit Design, 1990. As the circuit is basically a noninverting amplifier (Fig. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply. We can also make potential dividers from capacitors, but because a capacitor’s reactance is inversely proportional to its capacitance, a 10:1 capacitive divider requires the upper capacitor to be one-ninth the value of the lower capacitance. ? > 0 and −15 V when ν? In Figure 8.12(b) we see the small-signal model of the emitter-follower, including extended hybrid-pi values ro and rμ. Figure 4.10. When did organ music become associated with baseball? For the inverting configuration (Fig. why should input impedance be high in op-amps etc and output impedance be low??? What's the word equivalent to, "Announcement! What's the right way of removing an indoor telephone line? To get all the voltage from a source to a target without loss you need voltage bridging, that is a relative low output impedance to a higher input impedance. The collector current is related to the base-emitter voltage, vbe, via the all-important quantity gm, which is the transconductance of the transistor, having the units of Siemens (S). The separate convert-start input pin allows precise control over the sampling instant. The 1 MΩ resistor is the standard oscilloscope input resistance, and this is in parallel with the oscilloscope’s input capacitance and the lead capacitance. Note that in the case of a VIN with non-zero source impedance, such as a 50Ω signal source, it is beneficial to terminate the unused input with the same effective impedance to maintain balance. Ans: νo = α RIoexp(−e νi/kT); the orientation of the npn transistor is such that the input is at the emitter of the transistor. Why don't libraries smell like bookstores? It's the exact opposite for amp measurement, the internal impedance has to be as low as possible, otherwise, the global current of the branch you are monitoring will increase. By writing the circuit equations for Fig. How to remove Null plot markers in QuantilePlot? Time constants: We can view the upper resistor/capacitor combination as a high-pass time constant, and the lower resistor/capacitance combination as a low-pass time constant. For voltage summing, the resistance across the error voltage is increased; for current summing, the resistance through which the error current flows is decreased. Both BIFET and CMOS processes offer very high input impedance in any long-tailed pair configuration. (b) π-model. Measurements within switched-mode supplies are particularly prone to error from this problem, requiring minimised ground lead lengths, so faster probes allow their ≈150 mm flexible ground lead plus crocodile clip to be replaced by a stiff ≈50 mm probe. A reverse-biased photodiode in the circuit of Fig. If the input current i1 is not to exceed ±20 μ A, design the circuit for a gain of −100, that is, find R1 and RF. Are there any precedents to this? It has the value of the output impedance of the Thevenin (or Norton) equivalent circuit of the amplifier (see Section 2.2.4). Tutor-Rakshith Keesara In this video I explained why why input impedance should be high and output impedance should be low for an amplifier. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. 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