A Multi-cell Linear Power Amplifier for Driving Piezoelectric Loads
RAKESH K P
S-7 AEI
Roll No: 48
College Of Engineering , Trivandrum
2007-11 batch

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Introduction
Describes about multicell amplifier , developed by connecting floating signal modules in series to drive piezoelectric devices.


PIEZOELECTRIC devices or actuators have been used as positioners or driving motors in many fields such as optics, precision machining, and fluid control, as well as in optical disk drives
Voltage amplifiers are often used to drive piezoelectric actuators
Switching Amplifier
Linear Amplifier

Switching Amplifier
A setup stage is initially adopted to generate the constant high voltage required by the piezoelectric actuator.
The second stage is a half- or a fullbridge, which delivers the output voltage to the actuator as dictated by the reference signal.
LIMITATIONS

The bandwidth of the switching amplifier is limited

BENEFITS

It can establish an electric field in the actuator with minimal power loss and can recycle reactive
energy back to the power source.

Linear Amplifier
Higher bandwidth & slew rate

Linearity than a switching amplifier.
Less noise.
consumes more power than the
switching amplifier

MULTICELL AMPLIFIER
Developed by connecting floating signal modules in series to drive piezoelectric devices.
The amplifier generates a high voltage gain by summing the individual module gains. The bandwidth equals that of a single module.

FREQUENCY RESPONSE DUE TO CAPACITIVE LOADS
Capacitive loads commonly cause problems,


They can greatly reduce the o/P bandwidth and slew rate

The phase lag generated in the feedback loop
can cause the amplifier to oscillate.

FREQUENCY RESPONSE DUE TO CAPACITIVE LOADS :
Ro is the factor that most strongly influences.

The resistor Rs isolates the op-amp output and the feedback network from the capacitive load,potentially eliminating the oscillation or reducing ringing.

The combination of the isolation resistor and the load capacitor introduces a pole

Stability increases by increasing phase margin

Conclusion
Multicell amplifiers can be realized using low-voltage, high current, and high-power MOSFET devices or costly IC power amplifiers to achieve high output power.
Drawback - many isolated switching-mode power supply units are required to feed the individual cell of power
Advantages -multicell amplifier : Approximately constant corner frequency and the high common-mode rejection ratio, which offer the accuracy and linearity required for piezoelectric applications. Strong electrical isolation keeps high voltages away from equipment and reduces the risk of electrical shock.
The isolation resistance increases the damping ratio and reduces the outputm ringing.

REFERENCES
[1] A. J. Fleming and S. O. Moheimani, “Improved current and charge ampli-
fiers for driving piezoelectric loads, and issues in signal processing design
for synthesis of shunt damping circuits,” J. Intell. Mater. Syst. Struct.,.
[2] K. Furutani and K. Iida, “Performance of driving method of piezoelectric
actuator by using current pulse,” in Proc. 9th IEEE Int. Workshop
[3] A. J. Fleming and S. O. R. Moheimani, “Precision current and charge
amplifiers for driving highly capacitive piezoelectric loads,” Electron.