Figure 132 $V_{D D}=V_{S S}=1 \mathrm{~V}$ And $V_{t n}=-V_{t p}=0.4 \mathrm{~V}$ , and Assume That for All Transistors

Essay

Figure 13.2.1
It is required to design the folded-cascode op amp shown in Fig. 13.2.1. Let $V_{D D}=V_{S S}=1 \mathrm{~V}$ and $V_{t n}=-V_{t p}=0.4 \mathrm{~V}$ , and assume that for all transistors, $\left|V_{A}\right|=6 \mathrm{~V}$ . Design so that the power dissipated in the circuit (with no input signal applied) is $0.6 \mathrm{~mW}$ , and so that each of $Q_{1}$ and $Q_{2}$ is operating at a current four times that at which each of $Q_{3}$ and $Q_{4}$ is operating. Also, design so that all transistors operate at $\left|V_{O V}\right|=0.2 \mathrm{~V}$ .
(a) Show that the current drawn from each of the two power supplies is $2 I_{B}$ , and hence find $I_{B}$ and $I$ that result in the circuit operating at its specified power dissipation.
(b) Find the dc current at which each of $Q_{1}$ to $Q_{11}$ is operating. Present your results in a table.
(c) Find the input common-mode range.
(d) Find the required values of $V_{\mathrm{BIAS} 1}, V_{\mathrm{BIAS} 2}$ , and $V_{\mathrm{BIAS} 3}$ that result in the maximum allowable value of $v_{O}$ to be as high as possible.
(e) Find the allowable range of $v_{O}$ .
(f) Find the overall transconductance $G_{m}$ .
(g) Find the output resistance $R_{O}$ .
(h) Find the low-frequency voltage gain.
(i) If the amplifier at its output is modeled by a controlled current-source $G_{m} V_{i d}$ (where $V_{i d}$ is the differential input voltage) feeding the output resistance $R_{O}$ and the total capacitance at the output node $C_{L}$ , find the value of $C_{L}$ that results in the amplifier having a unity-gain bandwidth of $100 \mathrm{MHz}$ . Assume that the dominant pole is that formed at the output.