I'm having the following problem. I got to analyze a BJT differential pair with emitter degeneration of both transistors. I calculated the theoretical expressions of my gain and obtained (since the transistors are equal):
$$A_{d1}=-\frac{βR_{C}}{2(r_{π1}+(1+β)R_{E} )}$$
$$A_{d2}=\frac{βR_{C}}{2(r_{π1}+(1+β)R_{E} )}$$
The numerical values here don't matter for my question I guess. Then I proceeded to simulate my circuit LTSPICE. As I expected, the values were slightly different from the ones obtained theoretically. What I did not expect was that the values of the gains were slightly different from one another, while that transistor are equal (there should symmetry on the circuit). Why is this happening?
EDIT:
Here is the schematic used
as well as the operating point:
V(n001): 6 voltage
V(vo1): 2.9365 voltage
V(vo2): 2.9365 voltage
V(n003): -0.746863 voltage
V(n002): -0.653111 voltage
V(n004): -0.653111 voltage
V(n005): -5.32863 voltage
V(n006): -6 voltage
V(vc): 0 voltage
V(vd): 0 voltage
Ic(Q2): 0.00187503 device_current
Ib(Q2): 1.74223e-005 device_current
Ie(Q2): -0.00189245 device_current
Ic(Q3): 0.000928333 device_current
Ib(Q3): 9.18252e-006 device_current
Ie(Q3): -0.000937515 device_current
Ic(Q4): 0.000928333 device_current
Ib(Q4): 9.18252e-006 device_current
Ie(Q4): -0.000937515 device_current
Ic(Q1): 0.00179235 device_current
Ib(Q1): 1.74223e-005 device_current
Ie(Q1): -0.00180978 device_current
I(Rref): 0.0018272 device_current
I(Re2): 0.000937515 device_current
I(Re1): -0.000937515 device_current
I(Rc2): 0.000928333 device_current
I(Rc1): 0.000928333 device_current
I(Vc): -1.8365e-005 device_current
I(Vd): -9.18251e-006 device_current
I(Vee): 0.00370223 device_current
I(Vcc): -0.00368386 device_current
I notice that the current flowing in each of the voltage sources is a little bit different... Could that be the reason? And why are they different?