Definitions of Analog Multiplier

Definitions of Analog multiplier on the Web: * In electronics, an analog multiplier is a device which takes two analog signals and produces an output which is their product. Such circuits can be used to implement related functions such as squares (apply same signal to both inputs), and square roots.
Definitions of Frequency doubling on the Web: * Second harmonic generation (SHG; also called frequency doubling) is a nonlinear optical process, in which photons interacting with a nonlinear material are effectively "combined" to form new photons with twice the energy, and therefore twice the frequency and half the wavelength of the initial ...
ANALOG MULTIPLIERS/DIVIDERS
An analog multiplier/divider is a device that produces an output voltage or current that is proportional to the product of two or more independent input voltages or currents. In addition to multiplying and dividing, multipliers can perform squaring, square-rooting and modulation functions. Applications include radar, communications, and industrial controls where a real-time response is required. Analog Devices’ offers the widest selection of multipliers and dividers.

What Is Frequency Response?
Frequency response plots show the complex values of a transfer function as a function of frequency.
In the case of linear dynamic systems, the transfer function G is essentially an operator that takes the input u of a linear system to the output y:

For a continuous-time system, the transfer function relates the Laplace transforms of the input U(s) and output Y(s):

In this case, the frequency function G(iw) is the transfer function evaluated on the imaginary axis s=iw.
For a discrete-time system sampled with a time interval T, the transfer function relates the Z-transforms of the input U(z) and output Y(z):

In this case, the frequency function G(eiwT) is the transfer function G(z) evaluated on the unit circle. The argument of the frequency function G(eiwT) is scaled by the sampling