For unamplified detectors, what limits the minimum detectable signal?
For these detectors, the Johnson noise of the terminating resistance determines noise at the output of the detector. (These detectors are internally terminated at either 50 W or 100 W.) It is this noise, along with the responsivity, that determines the NEP we specify. In most applications, this noise is much less than noise added by subsequent amplifiers or measuring instruments, so you need to consider the entire system noise (along with the responsivity) to determine the minimum detectable signal. If you need high sensitivity, we recommend our 6-GHz or 12-GHz photoreceivers with built-in amplifiers, or, for higher-speed AC-coupled applications, you can use our Model 142X 20-GHz broadband traveling-wave amplifier with our Model 14XX 25-GHz detector.
