Calculate an analytical expression for the small-signal output resistance R_oof the bipolar cascode current mirror of Fig. 4.8. Assume that the input current source is not ideal and that the non-ideality is modeled by placing a resistor R₁in parallel with I_IN. Show that for large R₁, the output resistance approaches β₀ r_o/2. Calculate the value of R_oif V_CC= 5 V, I_IN= 0, and R₁= 10 k„¦, and estimate the value of V_OUTbelow which R_owill begin to decrease substantially. Use SPICE to check your calculations and also to investigate the β_Fsensitivity by varying β_Fbyˆ’50 percent and examining_IOUT. Use SPICE to plot the large-signal I_OUT-V_OUTcharacteristic.

Figure 4.8: Cascade current mirror with bipolar transistor

Transcribed Image Text:

Vcc IIN O l'oUT =lc2 Q2 Q4 Iga VOUT VIN