System realization (Circuit to implement block diagram)

Lecture D
Systems, design and example
• It is sometimes convenient to represent a set of
components as a system
• The components can be electrical, mechanical, thermal…
• Whatever their physical nature, we can think of the
components as being energy storage and energy
dissipation elements
• The energy can be electrical, mechanical, thermal…
• The system transfers energy to perform some task
Input-output relations
• The system has some input and some output
• The input is provided to the system from the environment
• The output is provided to the environment by the system
• The system itself becomes a “black box”
(Applied by external
environment to
(Provided by
system to external
• Demos:
– Tuning fork
– TV monitor (tuning fork input, impulsive input)
– DC motor
System modeling and analysis
• The system is often modeled as a mathematical
relationship between the input and output:
• Example: inverting voltage amplifier:
Notes on system modeling
• The definition of inputs and outputs can be
somewhat arbitrary
• Appropriate input, output definitions can simplify overall
• We sometimes start thinking of the system in terms
of the model governing the system
• It can be easy to forget that the system is a physical
• We may not even care whether the system is mechanical,
electrical, thermal…
• Example:
– DC motor output may be torque or motor speed
Example: Position control system
• “Plant” model:
Example: Position control system
• Block diagram of closed-loop control system:
System realization (Circuit to implement block diagram)
Signal conditioning circuit
• Circuit implementation:
• Frequency response:
• Demo acoustic sensor
– Low sensitivity, high noise
• Demo low-pass filter
– Higher sensitivity, reduced signal-to-noise ratio
• Frying pan analogy
System realization (Circuit to implement block diagram)
Difference amplifier
System realization (Circuit to implement block diagram)
• Demo closed-loop control