(a) A wideband MOS amplifier stage is shown in Fig. 7.48. Calculate the small-signal, low-frequency gain and use the zero-value timeconstant method to estimate the ˆ’3-dB bandwidth. Use μ_nC_ox= 60 µA/V², t_ox= 20 nm, C_ol= 0.3 fF/(µm of gate width), ψ_o= 0.6 V, V_t= 0.7 V, γ = 0.4 V^1/2, λ = 0, and V_O= 2.5 V dc. For C_dband C_sb, use C_db0= C_sb0=0.8 fF/(µm of gate width). Assume that the substrate is grounded. Compare your calculation with a SPICE simulation, and also use SPICE to estimate the second most dominant pole. Use SPICE to plot the small-signal bandwidth as the dc input voltage is varied from 0 to 5 V.

(b) Calculate the small-signal gain and ˆ’3-dB bandwidth including short-channel effects with ε_c = 1.5 × 10⁶ V/m. Assume the same bias currents as in (a) and model MOSFET short-channel effects with a resistor in series with the source. Connect the device capacitances to the lower end of the added source resistor.

Fig. 7.48:

Transcribed Image Text:

VDp = 5 V M2 Rs = 1 k2 100 C, = 100 fF V, M1 Vi