A n 2 k 2 0 k 1 2 2 k note for the inverting amplifier

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Unformatted text preview: g off at very low frequencies. Therefore, to make the op amp useful at higher frequencies, gain is traded for bandwidth. bandwidth. The Gain-Bandwidth Product (GBW) is given by: GBW = ANBW BW Example: For a 741 op amp, a noise gain of 10 k corresponds to a bandwidth of ~200 Hz Find: The GBW Find: GBW = 10 k * 200 Hz = 2 MHz GBW Cascaded Amplifiers - Bandwidth Cascaded Quite often, one amplifier does not increase the signal enough Quite and amplifiers are cascaded so the output of one amplifier is the input to the next. input The amplifiers are matched so: BWS = BW1 = BW2 = GBW GBW where, BWS is the bandwidth of all AN the cascaded amplifiers and AN is the noise gain the The Total Bandwidth of the Cascaded Amplifiers is: BWT = BWs(21/n – 1)1/2 where n is the number of amplifiers where that are being cascaded that Example: Cascading 3 Amplifiers with GBW = 1 MHz and A N = 15, Find: The Total Bandwidth, BWT Find: BWS = 1 MHz / 15 = 66.7 kHz BWT = 66.7 kHz (21/3 – 1)1/2 = 34 kHz Common-Mode Rejection Ratio Common-Mode The common-mode rejection ratio (CMRR) relates to the ability of The the op amp to reject common-mode input voltage. This is very important because common-mode signals are frequently encountered in op amp applications. encountered CMRR = 20 log|AN / Acm| Acm = AN log-1 (CMRR / 20) We solve for Acm because Op Amp data sheets list the CMRR value. The common-mode input voltage is an average of the voltages that The are present at the non-inverting and inverting terminals of the amplifier. amplifier. vicm = v(+) + v(-) 2 Common-Mode Rejection Ratio Common-Mode Example Given: A 741 op amp with CMRR = 90 dB and a noise gain, Given: AN = 1 k Find: The common mode gain, Acm Acm = AN log-1 (CMRR / 20) = 1000 1000 log-1 (90 / 20) = 0.0316 0.0316 It is very desirable for the common-mode gain to be small. Power Supply Rejection Ratio One of the reasons op amps are so useful, is that they can be operated from a wide variety of power supply voltages. be The 741 op amp can be operated from bipolar suppl...
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This document was uploaded on 03/31/2014.

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