A square law device is something where either current or voltage depends on the square of the other.
For example, a saturated MOSFET has I proportional to V^2.
A diode's characteristics also has a square but it's not as clean. It's exponential, and through a Taylor series you get linear, square, cubic terms....
Anyway, it's useful because you can use it as a modulator or mixer.
Adding voltages is easy (just use resistors or an op amp) but multiplying is hard. With a square law device like a MOSFET you can do this:
\(I \propto V^2\)
\(I \propto (sin(w_ct) + m(t))^2\)
\(I \propto sin(w_ct)^2 + m(t)^2 + m(t)sin(w_ct)\)
Now if you follow that with a bandpass filter centered on \(w_c\) you just get \(m(t)sin(w_ct)\)
Amplitude modulation.
Nice post, never thought of that.A square law device is something where either current or voltage depends on the square of the other.
For example, a saturated MOSFET has I proportional to V^2.
A diode's characteristics also has a square but it's not as clean. It's exponential, and through a Taylor series you get linear, square, cubic terms....
Anyway, it's useful because you can use it as a modulator or mixer.
Adding voltages is easy (just use resistors or an op amp) but multiplying is hard. With a square law device like a MOSFET you can do this:
\(I \propto V^2\)
\(I \propto (sin(w_ct) + m(t))^2\)
\(I \propto sin(w_ct)^2 + m(t)^2 + m(t)sin(w_ct)\)
Now if you follow that with a bandpass filter centered on \(w_c\) you just get \(m(t)sin(w_ct)\)
Amplitude modulation.
Howdy:Hey all, I've been studying up on mixers and stuff, but what exactly is a square law device and what is it useful for?