Your manager has requested you to review current techniques for reducing, or eliminating, the effects of external interference upon electronic circuits. He requires a short report in which you identify where circuits are particularly vulnerable to external interference. Identify potential sources of external noise together with possible solutions. Although the readership will be engineers, it is worth considering that they may not have the depth of understanding that your reading will have developed.
1. Discuss the internal noise sources that are present in a typical signal source and amplifier circuit, and describe their effects.
2. The company currently has a low noise amplifier circuit for which the LM4136 and the LMC6034 operational amplifiers are contenders. Determine the total noise generated for each and so recommend the best.
Some circuit details are as follows.
Signal source output impedance = 5k0
maximum input signal = 100 mV
bandwidth = 100 Hz to 10 kHz
system gain = 20 dB
Operating temperature = 17 0C
The data sheets for both amplifiers are attached, but may also be found in the National Semiconductor Operational Amplifiers Data sheets.
Connect a signal generator to an oscilloscope such that it is displaying a 4Vp-p, 500 Hz signal. Determine the signal to noise ratio and comment.
Take the output impedance of the signal generator to be 50 Ohms, and use it to estimate the thermal noise and thus its contribution to the total noise measured.