In ECL negative supply voltage is used because of

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In ECL negative supply voltage is used because of—

1. reduction in noise at the output means increase in CMRR
2. saving in power
3. eace of wired-OR operation
4. increase speed

Correct Option: A

As we know that CMRR is given by

CMRR =	A_d
	A_c

where, A_d = differential mode gain
A_c = common mode gain
A_d = V₁ – V₂
V₁ = input voltage at inverting terminal

A_c =	V₁ +V₂
	2

V₂ = input voltage at non-inverting terminal.
Since we require high CMRR (i.e., CMRR → ∞), which is possible with low Ac (i.e., as Ac → 0), which is possible when V₁ and V₂ must be of opposite sign. This is the reason why we use negative supply voltage in ECL logic circuits.