Multi-Stage Amplifier Configurations

What happens when non-ideal amplifiers are put in series?

What is the gain with two stages of gain A1 and A2 in series assuming RL = 1 MΩ?

• A1*A2

• A1+A2

• A1-A2

• A1/A2

What is the effect of inter-stage loading in DC-coupled multistage cascaded CE amplifiers?

What is the advantage of using complementary devices in amplifier stages?

What is the impact of using AC-coupled Common Emitter stages?

Design a Complementary Pair amplifier stage using 2N3904 and 2N3906 transistors (β =120, VBE =0.7v). Use a supply voltage of 10v and a source resistance of 15 KΩ. Estimate the DC bias voltages and currents, and compare these with the results of a computer simulation. Determine the small signal gain for a nominal 1 KHz signal.

The cascode is a two-stage amplifier composed of a single transconductance amplifier (usually a common source/emitter stage) followed by a current follower (usually a common gate/base stage). Compared to a single amplifier stage, this combination may have one or more of the following advantages: higher input-output isolation, higher input impedance, higher output impedance, higher gain or higher bandwidth.

If the cascode device stage were operated alone using its emitter or source as input node (i.e. common base/gate configuration), it would have good voltage gain and wide bandwidth. However, its low input impedance would limit its usefulness to very low-impedance voltage drivers.

Let us suppose that I need to build an amplifier that operates from a 100v power supply, however, the available transistors have a collector-to-emitter breakdown voltage (BVCEO) of only 25 volts. A cascode or a series of cascodes may also be combined with a voltage ladder to form a high-voltage transistor.

The Folded Cascode biasing techniques.