Analog multiplier

Under an analog multiplier, Eng. analog multiplier, electrical understands a component which forms the product of two analog signals. Multiplies related operations such as squaring and square root can be implemented on the basis of this function with the help of additional elements.

Function

A multiplier generally operates according to the function:

Or often with differential inputs and output offset correction:

Circuitry, the fact is exploited in the simple form of realization for a quadrant, that the multiplication of two positive factors on the logarithm of the two factors, and subsequent addition to the formation of the product to a final exposure can cause back:

This realized analog multiplier are suitable only for one quadrant, since the logarithm of a negative number is not real-valued. Extensions which allow a multiplication into four quadrants to work with a bias and based on the exponential transfer function of bipolar transistors. They are implemented in the form of the Gilbert multiplier in integrated circuits.

Basic structure

In the basic circuit of the analog multiplier shown on the right the two positive input voltages V1 and V2 are multiplied together to obtain the product in the form of the output voltage Vout. Resistors, all of the same value R to the operational amplifiers are assumed to be ideal, and the diodes have a reverse current Is, a thermal voltage VT ≈ 26 mV and an emission coefficient of n = 1 .2. After the summation at the point va then following voltage adjusts itself:

Is through exposure

Formed. The unwanted second term is compensated for by the last stage, an addition stage. What vout to:

Results.

There also exist other circuit variations, such as metal - oxide - semiconductor field-effect transistors. The product of the two input voltages to the positive, the output voltage V1 and V2 are formed in addition is still a constant positive reference voltage Vref required

Form.

Integrated multiplier

Often analog multiplier as an integrated circuit (IC ) for a specific application to be developed ( including RMS value calculation). In addition, there are a number of universal building blocks such as the AD834 from Analog Devices, a four - quadrant multiplier. Such universal building blocks often contain attenuator or amplifier circuits to the inputs and outputs, so that a signal can be scaled within the specified voltage limits.

Although analog multipliers have much in common with operational amplifiers, they are significantly more susceptible to disturbances such as noise and voltage offset (English offset), since they are multiplied by. In the high frequencies vibration tendencies are due to phase shift difficult to control. Therefore, the design of a universal broadband usable Analogmultipliziers is far more complex than that of a comparable operational amplifier. In their manufacture expensive special techniques such as laser trimming must be used. Thus such devices are expensive and are usually only used when there is no effective solution.

Demarcation voltage controlled amplifier to analog multiplier

The voltage input of a constant, the multiplier to scale the signal on the second input proportional to the height of the fixed voltage. In this case one speaks of a voltage knitted Your Tern amplifier. Obvious application areas are electronic volume and automatic gain control. Although often analog multipliers are used in such circuits, voltage controlled amplifier circuits are not necessarily the full analog multiplier. So in some ICs for electronic volume control allows the input to the control signal is often a higher input voltage at significantly reduced bandwidth.

In contrast, the inputs of a real multiplier are symmetric, ie have identical properties. The application of the real multiplier is used in the mixture or in circuits for the discrete Fourier transform.

As a four - quadrant multiplier is called a circuit can accept at the input and output signals of both positive and negative voltage values. Many multiplier circuits operate only two quadrants (one input has only one polarity ), or a quadrant, (inputs and outputs have only one polarity, usually positive).

Areas of application

  • Modulator
  • Demodulator
  • Discriminator
  • Mixer (Electronics )
  • Voltage controlled amplifier
  • Compander
  • Noise Reduction
  • Analog computer
  • Analog signal processing
  • Automatic Gain Control
  • RMS detection
  • Analog Filters

Withdrawal of the analog

The function of an analog multiplier can often be realized better with the help of digital technology in the form of a digital multiplier. Especially in the low signal frequencies digital solutions are cheaper and more effective, also an adaptation of the circuit function via software / firmware is possible. With increasing frequencies the cost of a digital solution to grow faster compared to the analog.

In addition, digital signal processing is still on the rise. This will always be other functions that applications of analog multipliers were originally taken over by digital signal processors such as the RMS detection of a signal.

Furthermore, many functions such as tone control and AGC using digital potentiometers can microcontroller -controlled circuits (see also digital to analog converter ) can be realized without the need for recalculation of the digitized value is required.

Nevertheless, the high potential of the analog speed at low cost is one reason for the use in RF technology as a modulator or demodulator, for example, as a mixer or RMS detection

Analogsignal Quadrant (plane geometry) Binary multiplier
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