Download Design and Development of a Low-Noise Amplifier: A Laboratory Experiment for ECE Students and more Lab Reports Electrical and Electronics Engineering in PDF only on Docsity! Low-Noise Amplifier Design ECE 6416 Georgia Institute of Technology October 29, 2003 Abstract Design and verification of a low-noise amplifier with electrical isolation between the sensor and load. 1 Objective The objective of this experiment is to design, simulate, evaluate, and document a low-noise amplifier circuit. 2 Specifications A basic circuit diagram of the amplifier is shown in Fig. 1. The low-noise amplifier is to have one input and one output. The amplifier is to employ a unipolar + 9V or +15V dc power supply. A 4N25 electro-optical isolator is to be used to isolate the source from the load. The source resistance of the sensor is to be Rs = 6.8 kΩ. A preamplifier is to be used between the sensor and the isolator and a post amplifier between the isolator and load. The active devices used in these two amplifier will be discrete transistors. The load resistor is to be RL = 12 kΩ. The maximum value of the amplitude of the open circuit voltage produced by the sensor is to be 10mV. The sensor drives a preamplifier which is ac coupled to the electro-optical isolator. The output of the isolator is amplified by the post amp to supply the output signal to the load resistor. The post amp should contain a coupling capacitor to keep dc off the load. 3 Design Goals • The maximum output SNR ≥ 50 dB (Vso/Vno) with an input signal of 10mV peak sine wave at a frequency of 3.2 kHz. 1 Figure 1: Simplified schematic of the amplifier. • Midband voltage gain of 40 dB ±1 dB. • No visible distortion on sine wave output • Upper and lower −3 dB frequencies of 500Hz and 20 kHz. • Minimum noise. 4 Devices Discrete transistors are to be used to implement both the pre and post amps. The choices should be restricted to those normally stocked (2N4401 and 2N3904 NPN BJTs, 2N4403 and 2N3906 PNPs, 2N5457 N Channel JFET, and 4007 MOSFETs). The electro-optical isolator is to be a 4N25. This is a Dual In-Line package with pinouts shown in the circuit diagram. It contains a GaAs LED which produces light as a function of the current passing through it. A photo transistor is placed in the same package which has a base current that is a function of the light striking it and the dc bias current. Thus the base may be either biased or left dangling (unconnected). Data sheets for all of these devices are readily available on the internet. 2
