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'CHAPTER '6
LOG X DIODE FUNCTION GENERATORS
6.1
INTROPUCTION
The Log X DFG's operate in conjunction with an operational amplifier to produce
an output voltage that is proportional to the logarithm of the input voltage •
. Common and natural logarithms and antilogarithms can be generated.
The inputs and'outputs for the circuit conf{gurations described in the following
paragraphs arel given on a
u~it-scaled
basis.
Computer reference is taken as
basic unit of measurement so that all properly scaled voltages are
~1.0
unit in
magnitude.
A
description of unit-scaling and a tabulation of outputs for both
unit-scaling and voltage-scaling is given in Appendix 4.
6.2
OPERATING CONSIDERATIONS
The Log X DFG, Model
0.,~6.0355,
consists of four independent logarithmic function
generators.
Two of the generators accept a positive input voltage X and produce
an output voltage of -1/2 10glO (-IOOX).
The other two generators accept a neg-
ative input voltage X and proauce an output voltage of 1/2 10glO C:"lOOX).
NOTE
The abbreviation log indicates the logarithm
to the base 10.
The abbreviation In is used
for natural logarithms (to the base e).'
A simplified schematic of the 10g.X DFG is shown in Figure 6.1.
The four
DFG'~
are .independent and each has a resistor associated with it.
The log X DFG
patching terminations occupy the left side of the patch block.
The right side is
occupied by two MDFG amplifier patch terminations and two diodes and a 100 ohm
resistor used as free components.
The MDFG amplifier patch terminations are
described in Chapter 8.
6.3
OPERATING INSTRUCTIONS
The patching for the DFG's is illust'rated in Figure 6.2.
Note that the input
voltage is restricted to a range'of 0.01 to 1.0 (reference).
Since the DFG has
a variable input impedance, input voltages should never be obtained from potenti-
omet~rs.
Care should be taken not to apply an input voltage of the wrong polarity.
Although doing so wiil not harm the DFG, it can constitute a severe overload on
the associated amplifiers in certain circuits.
6-1
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