Due Wednesday Feb 20 at the start of class

Figure 1. Folded cascode amplifier
Figure 2. Folded cascode amplifier — AC equivalent circuit

## 1. Draw the small-signal equivalent circuit

(this was done in-class Monday)

## 2. Linear circuit analysis

Consider the three capacitors `Cin`, `Cb`, and `Cout` as “BFC’s” — i.e. large enough to be effectively short circuits at all signal frequencies. It will be acceptable to ignore $r_o$ (consider an open circuit) for `Q2`, it has little numerical influence in this circuit. Use this small-signal equivalent circuit to find symbolic solutions for:

• $v_2$ as a function of $v_1$

• $v_{out}$ as a function of $v_2$

• $v_{out} / v_{in}$

• $v_{out} / v_{s}$

Use the resistor values determined from Homework 07 to compute the transistor small-signal parameters $r_\pi$, $r_o$, and $g_m$ for each transistor with the help of Tour Book Table 4. Small-signal parameters and Tour Book Table 2. Transistor parameter definitions . Then compute the overall amplifier’s small-signal input and output resistances and open-circuit voltage gain. Remember that the definition of Av0 is the voltage gain from $v_{in}$ (not `Vs`!) to $v_{out}$ with the load disconnected.

For help determining where, exactly, the amplifier input and outputs are, consider capacitors `Cin` and `Cout` as connecting the signal source and load to the amplifier’s proper input and output, respectively.

Table 1. Folded cascode amplfier major parameters
Device Value (units)

Rin

Rout

Av0

You can cross-check these values by computing them via a different route by using the “table technique” with Tour Book Table 6. Bipolar transistor amplifier types. They should also match your measurement results for Lab 3-B.