Classical infrared mixing with solid state diodes

It is shown that classical infrared diode mixing can compete with straight quantum detector diodes even if the available power gain of the diode mixer is as small as 10^?5–10^?6. To shed light on the diode mixer problem, the small signal diode detector problem is discussed, the effect of the series resistance r of the diode is dealt with and the time constants that may be operating in the device are evaluated. It is shown that Schottky barrier diodes operating in the diffusion mode are probably too slow, even though the response problem has not been solved exactly. Schottky barrier diodes operating in the thermionic mode are better; they can be understood in terms of a vacuum tube analogy, indicating that the characteristic time constant is the transit time of those electrons that just pass the barrier. Diodes operating in the tunneling mode have probably the fastest response, but an exact theory has not been developed. An interesting series resonance method is discussed that may lead to improved detector response near the resonance frequency.