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RF Electronics Chapter 10: Operational Amplifiers Page 357 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 10.20. Gain and noise figure of different OpAmps. Figure 10.20 shows the gain and noise figure performance for several high frequency low noise OpAmps from different manufacturers. The circuit used are the same as figure 10.18, but with Rg =10 Ω and Rf =1 kΩ, resulting in a 40 dB voltage gain, so that 3dB bandwidths in excess of 30 MHz can be obtained. In addition, the supply voltages are changed to match those used for the test circuits in the OpAmp data sheets. Figure 10.20 shows that noise figures of less than 1.5 dB can be obtained from 1 kHz to 100 MHz. In many cases, the Spice files will import directly. In some cases, the file extensions need to be renamed to .cir to allow Cadence AWR DE to convert the PSpice files. Several high frequency low noise amplifiers, like the AD8099, have power-down pins, which at this stage cause problems in importing the PSpice files into AWR DE. Oscillator using Operational Amplifiers Since OpAmps can be used to frequencies above 100 MHz, OpAmps can be used for oscillators. Chapter 6 describes the design procedure for oscillators. A Colpitts resonator is slightly cheaper since only one inductor is used. In both the Colpitts or Hartley oscillators, one capacitor in the resonator can be replaced with a varactor diode, to produce a Voltage Controlled Oscillator (VCO). The correct DC biasing on the OpAmp pins is required and it is desirable not to have a short circuit path at DC between the output and ground, since any DC offset on the output will then cause current limiting or failure in the OpAmp. To gain some understanding of the fundamental limitations, a linear OpAmp model (OPAMP) is used and output limiting is applied by using back to back diodes to clip the output. A Spice model SDIODE, which includes noise, is used. Figure 10.21 shows the circuits for two 10 MHz oscillators using this linear OpAmp model. A Hartley oscillator is shown on the left and a Colpitts oscillator is shown on the right. The OSCTEST element in the left circuit is used for the linear oscillator analysis to verify that the correct gain and phase shift occurs. The OSCAPROBE element in right circuit is used for the non- RF Electronics: Design and Simulation 357 www.cadence.com/go/awr