The document discusses log and antilog amplifiers using diodes and transistors, as well as the concept of virtual ground in electronics. A virtual ground is defined as a circuit node maintained at a steady reference potential that aids in circuit analysis, especially in operational amplifiers. The document also emphasizes the relationship between the voltage at the inverting and non-inverting inputs of an op-amp under specific conditions, referring to this characteristic as a virtual short.

1. Module III
Log amplifiers
Antilog amplifiers

2. Fundamental equations - Diode
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3. Fundamental equations - Diode
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4. Basic log amplifier using diode
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5. Basic Antilog amplifier using diode
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6. Fundamental equations - Transistor
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8. Basic Log amplifier using transistor
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9. Basic antilog amplifier using transistor
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11. Concept of virtual ground
• Virtual (adjective): almost or nearly as described, but not
completely or according to strict definition.
• In electronics, a virtual ground is a node of a circuit that is
maintained at a steady reference potential, without being
connected directly to the reference potential.
• In some cases the reference potential is considered to be that of the
surface of the earth, and the reference node is called "ground" or
"earth" as a consequence.
• The virtual ground concept aids circuit analysis in operational
amplifier and other circuits and provides useful practical circuit
effects that would be difficult to achieve in other ways.
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12. Concept of virtual ground (Contd…)
• We can calculate the voltage at the inverting input of the
Opamp in reference to the ground. The calculated (or
measured) voltage is negligible or “virtually” the same as the
ground, hence a virtual ground.
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13. Concept of virtual ground (Contd…)
• The voltage of the inverting input will always follow the voltage of
the non-inverting input in an Opamp working under this conditions,
therefore a far better terminology for this characteristic should
be virtual short
• By no means we can find a virtual ground on the above circuit, but
the voltage difference across the inputs of the amplifier is virtually
zero, if the operating conditions are preserved.
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14. References
• https://www.quora.com/What-is-meant-by-virtual-ground-in-
an-op-amp
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