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RF Electronics Chapter 10: Operational Amplifiers Page 353 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Example 10.2: Amplifier Design for Noise Performance. A microphone has a source impedance R s = 600 ٠and requires a load resistance larger than 1 k٠for the microphone to operate correctly. The normal output from the microphone is 1mV. An amplifier with a voltage gain of close to 1000 is required. Figure 10.17 shows the circuit diagram of the non-inverting amplifier circuit. In practice, coupling capacitors are used at the input and output, to ensure that the amplifier output clips symmetrically and that no DC offset voltage occurs at the output. Rg should be such that it is much larger than the resistance of tracks used in the PCB or the resistance between the grounded side of Rg and the common ground point of the amplifier. Rg should be small to minimise the thermal noise of the resistor, which is amplified by the amplifier gain. Figure 10.17. Non-inverting amplifier. For the non-inverting amplifier, the noise power at the output of the OpAmp due to each component is evaluated using equations 10.13 to 10.20, [4, 10, 11]: OpAmp noise voltage � �� � � �� � � �� � � � � � Eqn. 10.13 OpAmp noise current +in �� ��� �� � � � � � � �� � � � �� � � �� � � � � � Eqn. 10.14 OpAmp noise current -in �� ��� �� � � � � � � �� � � � �� � � � � � � Eqn. 10.15 Resistor Rs noise � ������ � � � � � � �� � � � �� � � � � � Eqn. 10.16 Resistor Rt noise � ������ � � � � � � �� � � � �� � � � � � Eqn. 10.17 Resistor Rg noise � ������ � � � � � � � � Eqn. 10.18 Resistor Rf noise � ������ � Eqn. 10.19 OpAmp Voltage Gain � �� � � � � �� � � � �� � � � Eqn. 10.20 RF Electronics: Design and Simulation 353 www.cadence.com/go/awr

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