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RF Electronics Chapter 10: Operational Amplifiers Page 355 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. OpAmp Voltage Gain � ��� � � � � �� � Eqn. 10.27 These equations are included in the project files for figures 10.17 and 10.18. This allows the noise contribution of each noise source to be determined and component values to be tuned to minimise the noise, whilst maintaining practical component values. To compare the noise performance, these equations are also entered in a spreadsheet, the results of which are presented in table 3. For this example T = 290 Kelvin and the bandwidth B = 20 kHz. For Voltage feedback amplifiers, the +ve input noise current (i np ) is normally the same as the –ve input noise current (i nn ), however for current feedback amplifiers, they are normally different since the +ve and –ve input circuit architectures are different. Table 10.2 shows that for the AD8000, the –ve input current noise is 26 pA/Hz and the +ve input current noise is 3.4 pA/Hz. In figure 10.14, the +ve and –ve input current noise is assumed to be the same, (i ni ). Table 10.3. Noise for inverting and non-inverting amplifier configurations. Operational amplifier Noise calculation Temperature 290 4kT 1.60E-20 Bandwidth (Hz) 20000 Rs Source resistance Rt Resistance to ground at non-inverting input Rg Input resistance series with inverting input Rf Feedback resistor Op Amp AD 797 Non Inverting Op Amp Inverting Amp Value Output Noise Value Output Noise en nV 0.9 1.623E-08 0.9 1.620E-08 in+ pA 2.0 2.851E-08 2.0 8.000E-12 in- pA 2.0 8.000E-12 2.0 2.044E-07 Rs 600 1.903E-07 600 1.922E-07 Rt 1.00E+05 1.142E-09 1.00E+01 3.210E-09 Rg 10 3.203E-09 1.00E+03 3.203E-07 Rf 10000 3.203E-12 1.60E+06 5.125E-10 Gain (FB) 995 1000 RInp (Rsn//Rtn) 596.4 Ripp (Rgn//Rfn) 9.99 1.598E+03 Total Power/Hz 1.20E-11 3.68E-11 Total Noise Power 2.39E-07 7.37E-07 Noise Voltage mV 4.89E-01 8.58E-01 Signal In Out mV 1 995 1 1000 SNR 66.17 61.33 Noise figure dB 1.00 5.84 Noise figure 1.26 3.83 The ADA4898 includes a power down switch, which causes simulation errors in Cadence AWR DE. So for the calculations in table 10.3 and simulation in figure 10.19, an AD 797 OpAmp is used, since it is suitable and its Spice model include input voltage and current RF Electronics: Design and Simulation 355 www.cadence.com/go/awr