As you may already know, some very low frequency noises (0.1Hz-10Hz) can’t be measured by an oscilloscope. Our specially designed circuit amplifies these low noises so that the value can be acurately determined, and thus entered into a datasheet. This circuit is designed to amplify low frequencies using it's range from a 0.1Hz second order high pass filter to a 10Hz forth order low pass filter. Since the internal noise of the amplifier will also influence the testing result, the noise coefficient is reduced in order to improve the output ratio of signal power VS. noise power.
The ideal amplifier noise coefficient is F = 1 (0 db); meaning the output ratio of signal power VS. noise power is equal to the input ratio. A well-designed low noise amplifier FN can reach over 3 db. When testing low noise figures, use temperature (Te) as in amplifier noise performance metrics: Te = T0 (F - 1). Here, both the unit of noise coefficient and the noise temperature are in kelvin (K) when it's under ambient temperature.
The signal that the circuit receives might be very weak, so it's the low noise amplifier's job to amplify it. The strength of the noise might also change, due to interference by stronger signals in the transmission path. Therefore, this amplifier has a large linear range and adjustable gain functions.
For more information, please visit: http://www.analogtechnologies.com/High_Current_Low_Pass_Filter.html