A differential circuit employing active loads is shown in Fig. 7.42. Bias voltage V_Bis adjusted so that the collectors of Q₁and Q₂are at +5 V dc. Biasing resistors are R_B1= 10 kΩ and R_B2= 20 kΩ. Calculate the low-frequency, small-signal voltage gain Ï…_o/Ï…_i, and use the zero-value time-constant method in the DM half-circuit to estimate the ˆ’3-dB frequency of the DM gain. Use the device data in Problem 7.25.

Data from Prob. 7.25:

Data: npn: β = 100, f_T = 500 MHz at I_C = 1 mA, C_μ0 = 0.7 pF, C_je = 3 pF (at the bias point), C_cs0 = 2 pF, r_b = 0, and V_A = 120 V. Assume n = 0.5 and ψ₀ = 0.55 V for all junctions. pnp: β = 50, f_T = 4 MHz at I_C = ˆ’0.5 mA, C_μ0 = 1.0 pF, C_je = 3 pF (at the bias point), C_bs0 = 2 pF, r_b = 0, and |V_A| = 50 V. Assume n = 0.5 and ψ₀ = 0.55 V for all junctions.

Fig. 7.42:

+10 V VR Q4 o Vo 20 k2 20 k2 O2 w- Rg2 O5 RB1 -10 V