For a 1 k? resistor at room temperature and a 10 kHz bandwidth, the RMS noise voltage is 400 nV . A useful rule of thumb to remember is that 50 ? at 1 Hz bandwidth correspond to 1 nV noise at room temperature.
12.
By superior layout and circuit design made possible by Bresee's and Khadders superior process uniformity, transistor performance, and surface passivation, Erdi was able to design and achieve breakthrough advances in micro power amplifiers with both low input offset and 1 / f noise voltage rivaling many chopper amplifiers formerly used exclusively for micro volt input amplifiers.
13.
Noise is a random process, characterized by resistive element is proportional to the square of the voltage across it, noise voltage ( density ) can be described by taking the square root of the noise power density, resulting in volts per root hertz ( \ scriptstyle \ mathrm { V } / \ sqrt { \ mathrm { Hz } } ).
14.
Pre-amplifiers designed for high input impedance may have a slightly higher effective noise voltage at the input ( while providing a low effective noise current ), and so slightly more noisy than an amplifier designed for a specific low-impedance source, but in general a relatively low-impedance source configuration will be more resistant to noise ( particularly mains hum ).
15.
It therefore adds 1 / 10 of the noise power caused by the source, and the noise figure is 0.4 dB . For a low-impedance source of 250 ?, on the other hand, the noise voltage contribution of the tube is 10 times larger than the signal source, so that the noise power is one hundred times larger than that caused by the source.
