last time never ended

1. Sketch the plot

diff pair bjt basic
Figure 1. Basic bipolar differential pair
From Tourbook 7.2. Bipolar differential pair.
\[i_1 = \dfrac{I_{tail}}{1 + \exp\left(\frac{-(v_1 - v_2)}{V_T}\right)}\]
\[\text{with}\quad v_d = \left(v_1 - v_2\right)\nonumber\]

Plot \(i_1\) and figure out what \(i_2\) is.

2. Simulate the pair

CircuitLab simulation

diff cm sources
Figure 2. Simulating with CM and DM voltages

Figure 2 is the conceptual set up of setting voltages at two nodes vA and vB by instead stating as common-mode and differential voltages.

Use KVL to find:

vA =

vB =

The lower figure shows how to use a pair of voltage-controlled voltage sources VCVS to set vA and vB. The advantage is that both sources vD and vCM are single sources, which is much more convenient for using as simululation stimuli.

Before simulating: if all input sources are 0 V, what is the DC voltage at outA and outB?

  • Plot (DC sweep): (vA, vB) vs. vCM

  • Plot (DC sweep): (vA, vB) vs. vD

Pay attention to V(E).

  • Plot (DC sweep): (outA, outB) vs. vCM.
    How does this make sense?

  • Plot (DC sweep): (outA, outB) vs. vD

Input sinewaves instead and plot as voltages versus time. 3 periods with a time step smaller than 1/100th of a period.

Change the input sinewave amplitude so the output voltages clip.