I am currently investigating semiconductor superlattices and I am analyzing the negative differential velocity (NDV) after a certain limit. I understand how NDV leads to negative power, but I am struggling to see how this leads to signal amplification?

Any help or 'points in the right direction' would be greatly appreciated!


  • $\begingroup$ I'm not particularly familiar with superlattices, but presumably power is defined positive when work is done on the lattice (through something like electron hole pair generation), and work is usually done by an electrical signal. Doesn't negative power imply amplification almost by definition? $\endgroup$
    – David
    May 1, 2016 at 9:46
  • $\begingroup$ Thanks for the reply! I wasn't sure if there was a major step I was missing to link this together. Thankyou for pointing out this is by definition, much appreciated. $\endgroup$
    – Dan
    May 1, 2016 at 18:21
  • $\begingroup$ Glad I could help :) $\endgroup$
    – David
    May 1, 2016 at 21:27

1 Answer 1


Too many words.

Signal amplification is a fact. Negative power is an attempt to clarify a concept of stray reactances leading to a mathematical solution known as a "power factor" - not a fact.

"P:ower" refers to the ability to perform work when force(pressure/voltage) is combined with the capacity to deliver "energy" (electrical current. or current of water or flow of air). In electrical terms Power is defined as

volts x amps.

When dealng with alternating-currents the definitions must be modified

instantaneous power = instantaneoas voltage x instantaneous current

but the presence of (stray) reactances causes the waveforms of voltage and current to lose synchrony (they develop a difference in relative phase). Now multiply values of instantaneous voltag and current, plot them as a graph and you have a sinewave


note that this is a graphical representation of a mathematical function and has no entity as a waveFORM.

The relative phase-shift is referred to as a "power factor" which expresses the ratio between "DC-power" and "AC-power" and it pleases some to regard the lower half-cycles of that graph as representing "negative power"..

In truth the concept can be useful especially when makimg measurements with an ac-bridge. Be careful not to fall into the easy trap of forgetting that you are desling with "short speak".

To cvcalculate he gain provided by an amplifier requires a venture into Algebra and the technique varies depending on thr amplifier concerned is a voltage-Amp, a current-amp or a power-amp.

Follow through the algebraic procedure and find that you are confronted with parts of the circuit where increasing (say) the voltage causes a decrease in current ... a negative value for the circuit resistance. But that is only in the world of mathematics.

  • $\begingroup$ I think you missed the whole point that the question was about semiconductor physics. Your answer is really off topic. $\endgroup$
    – David
    May 1, 2016 at 9:54
  • $\begingroup$ David Afraid I have to disagree.t o me your queston qwas about nwegatgive poqwwer $\endgroup$
    – Ken Green
    May 1, 2016 at 14:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.