1 Analog versus Digital Information-bearing signals can be either analog or digital. Analog signal takes on a continuous range of amplitude values. Whereas digital signal takes on a finite set of discrete values (often binary) and frequently changes values only at uniformly spaced points in time Analog circuits:  circuits that connect to, create and manipulate arbitrary electrical signals  circuits that interface to the continuous-time “real” word Analog and digital signal can be converted to each other Relative advantage:  digital circuits are more immune to noise  digital circuits tend to be easier to implement with IC (integrated circuit) technique  digital systems are more adaptable to a variety of use

2 So why do we still study analog? The real world is analog Many of the inputs and outputs of electronic systems are analog signal Many electronic systems, particularly those dealing with low signal amplitudes or very high frequency required analog approach The dominance of digital circuits actually increased the amount of analog electronics in existence Nowdays, most electronic systems contain both analog and digital (called Mixed-signal, also Mixed-signal SoC (System on Chip)) Lots of most challenging design problems are analog Good analog circuit designers are scarce (very well compensated, gain lots of respect, regarded as “artists” because of the “creative” circuit design they do…)

3 Electronic system design process System specification Topology synthesis Constraint transformationLayout generation Transistor sizing Topology selection Yes No Design verification Meet specification Next iteration Circuit verification Meet specification No End Yes Next iteration System functionality Solution approaches Design system block diagram including block specifications Design each block Construct prototype Test prototype Production Our interest lies here

4 Basic amplifier concepts Amplification of low amplitude signal is one of many functions that is best handled by analog circuits We need amplifiers Ideally, an amplifier produces an output signal with the same waveshape as the input signal, but with a larger amplitude Output signal, where is called the voltage gain of the amplifier.

5 Voltage amplifier model A voltage amplifier should have a large input impedance and a small output impedance is the open circuit voltage gain, the actual gain is different if impedance are non-ideal There are also other models to model the gain property of the amplifiers, e.g. current-amplifier model, transconductance-amplifier models and transresistance- amplifier models Voltage amplifier transconductance-amplifier model

6 A few other important concepts Any electrical signal can be considered to consist of a sum of sinusoidal components having various frequencies, phases and amplitudes. (Spectrum?) Amplifier gain is complex (which changes both the amplitude and phase of the input signal) Amplifier gain is a function of the frequency (so it is important to the frequency characteristic of the input signal) Differential input amplifiers have two input sources Real amplifiers also respond to common mode signal. The gain for common mode signal is denoted as, the output of the differential amplifier is then and the ratio is called common mode reject ratio (CMRR) Differential amplifier Noninverting terminal Inverting terminal