Amplification Noise

The source noise generated by a feedback amplifier, from [#horohill##1#], is a function of some noise parameters of the op-amp, and the values of the feedback network. In Equation #eqnampnoise#274>, #tex2html_wrap_inline1318# is the noise voltage squared per hertz, #tex2html_wrap_inline1320# is the voltage noise from the amplifier, and #tex2html_wrap_inline1322# is the current noise. #tex2html_wrap_inline1324#, for an inverting amplifier, is calculated as:

#equation275#

Using values for a typical low noise op-amp (#tex2html_wrap_inline1326#) at an inverting gain of 10, the total input referred noise is approximately 30 #tex2html_wrap_inline1328#. This represents roughly as much noise power per hertz as there is thermal noise total. In practice, a higher noise op-amp was used which had a total input referred noise voltage of approximately 150 #tex2html_wrap_inline1330#.