ECL 10k OR/NOR回路
ECL uses a differential pair as a current-steering switch. The specifications for the input and output voltages are Vih,Voh ≈ −0.9V and Vil, Vol ≈ 1.75V. Any transistor won't go into saturation if the input voltage complies with the specification.
The circuit below is an ECL OR/NOR gate called ECL 10k series. V1 and V2 are the inputs, and VR (=1.32V) is the reference voltage. The differential pair doesn't work ideally because the tail current is set by a resistor (R3) rather than a current source.
Assuming VBE(ON)=0.75V, if both V1 and V2 inputs are low (=−1.75V), Q1 and Q2 turn off, and the operation point is:
I(R3) ≈ 4mA
V(R1) ≈ −0.05V, depending on the load current
V(R2) ≈ 1V
V(nor) ≈ −0.9V, depending on the load current
V(or) ≈ -1.75V
If either V1 or V2 is high (=−0.9V), Q3 turns off, and the operation point is:
I(R3) ≈ 4.6mA
V(R1) ≈ −1V,
V(R2) ≈ −0.05V, depending on the load current
V(nor) ≈ −1.75V
V(or) ≈ -0.9V, depending on the load current
Note that R3 is not a constant current source. Its current changes according to the inputs. Thus diffrent values are set for R1 and R2 to achieve the specified output voltage.
Ref. Sedra and Smith, Microelectronic Circuits