Analog Multiplier - The Analog Vs. Digital Tradeoff in Multiplication

The Analog Vs. Digital Tradeoff in Multiplication

In most cases the functions performed by an analog multiplier may be performed better and at lower cost using Digital Signal Processing techniques. At low frequencies a digital solution is cheaper and more effective, and allows the circuit function to be modified in firmware. As frequencies rise, the cost of implementing digital solutions increases much more steeply than for analog solutions. As digital technology advances, the use of analog multipliers tends to be ever more marginalised towards higher-frequency circuits or very specialized applications.

In addition, most signals are now destined to become digitised sooner or later in the signal path, and if at all possible the functions that would require a multiplier tend to be moved to the digital side. For example, in early digital multimeters, true RMS functions were provided by external analog multiplier circuits. Nowadays (with the exception of high-frequency measurements) the tendency is to increase the sampling rate of the ADC in order to digitise the input signal allowing RMS and a whole range of other functions to be carried out by a digital processor. However, blindly digitizing the signal as early in the signal path as possible costs unreasonable amounts of power due to the need for high-speed ADCs. A much more efficient solution involves analog preprocessing to condition the signal and reduce its bandwidth so that energy is spent to digitize only the bandwidth that contains useful information.

In addition, digitally controlled resistors allow microcontrollers to implement many functions such as tone control and AGC without having to process the digitised signal directly.