In the Anti-logarithmic Amplifier IC the output voltage is proportional to the log or to the exponential function (antilog) of the input signal. Most logarithmic amplifier ICs are available with an external strapping option that makes them operable in either the algorithmic or the exponential (antilog) mode, as indicator in figure 1. The antilog element consists of semiconductors stage in which the input voltage procedures a current that is an exponential function. To produce a logarithmic output, the antilog element is connected as part of the feedback circuit as shown in figure 1, while figure 2 shows the connection for producing an exponential output function.
Key Parameters of Anti-logarithmic Amplifier IC
- Log conformity error: Indicates the derivation of the output from a straight line when plotted on semi log paper, after adjustment for offset voltage, reference voltage and current factors, and other variants.
- Offset voltage and current: Must be adjusted for a minimum in order to obtain a logarithmic function over the entire dynamic range.
- Reference voltage and current: Adjustment of this internally generated voltage and current is essentially the same as in most operational amplifier.
- Gain Factor: External strapping connections are usually available to provide different amounts of amplification and therefore different logarithmic or exponential gain factors.
Figure 1: Anti-logarithmic Amplifier IC with antilog element in feedback
Figure 2: Anti-logarithmic Amplifier IC with antilog element in input
Applications of Anti-logarithmic Amplifier IC
The compression of any wide-range input signal, analog computing circuits, linearization of exponential sources, such as transducers, certain types of audio circuits, compression and expansion circuits for voice communications.
Representative Part Number: Analog Device Model 755
Check out the article on Antilogarithmic amplifier derivation
Components:
A relatively specialized device, a logarithmic amplifier can perform a variety of useful functions provided the key parameters are selected correctly for the particular application.