Does anyone know the basic properties of the following four op amp.
I know Current Amplifier has a
Low Input Impedance
High Output Impedance
but how about
Voltage Amplifier
Transconductance
Transresistance
Ed
I know Current Amplifier has a
Low Input Impedance
High Output Impedance
but how about
Voltage Amplifier
Transconductance
Transresistance
Ed
voltage amplifier:
high input impedance
low output impedance
(drive with a voltage source, get voltage out)
transconductance amplifier:
high input impedance
high ouput impedance
(drive with a voltage source, get current source
out)
transimpedance amplifier
low input impedance
low output impedance
(drive with a current source, get voltage out)
Erik
high input impedance
low output impedance
(drive with a voltage source, get voltage out)
transconductance amplifier:
high input impedance
high ouput impedance
(drive with a voltage source, get current source
out)
transimpedance amplifier
low input impedance
low output impedance
(drive with a current source, get voltage out)
Erik
When do you use each cause
Hi Erik
The output impedance you're refering to is the overall circuit and not the op amp itself right.
so do you know under which case do we use what?? For example say erm you would have to make a voltage amp from an op amp with a high input impedance and a low output impedance that would give a gain of erm say 23. Which Feedback would you use in this case and why??
Ed
Hi Erik
The output impedance you're refering to is the overall circuit and not the op amp itself right.
so do you know under which case do we use what?? For example say erm you would have to make a voltage amp from an op amp with a high input impedance and a low output impedance that would give a gain of erm say 23. Which Feedback would you use in this case and why??
Ed
definitions
Reciprocals:
Resistance
Conductance
Reactance Susceptance
Impedance Admittance
Ratios:
V/V voltage gain, no units
V/I resistance or impedance, ohms
I/V conductance or admittance, mhos or siemens
I/I current gain or beta, no units
A trans[ratio] amplifier converts ratio denominator (input) to the ratio numerator (output).
Input and output impedances are not defined by the type of amplifier, they can be anything. In general a current input will have lower Z than a voltage input and a current output will have higer Z than a voltage output.
Reciprocals:
Resistance
ConductanceReactance
SusceptanceImpedance
AdmittanceRatios:
V/V voltage gain, no units
V/I resistance or impedance, ohms
I/V conductance or admittance, mhos or siemens
I/I current gain or beta, no units
A trans[ratio] amplifier converts ratio denominator (input) to the ratio numerator (output).
Input and output impedances are not defined by the type of amplifier, they can be anything. In general a current input will have lower Z than a voltage input and a current output will have higer Z than a voltage output.
Re: When do you use each cause
Hi, Ed,
Yes, that is right. It is the influence of the feedback network that causes the impedance to change.
Here are the 4 basic feedback arrangements. Which one you would want to pick depends on what is feeding the circuit and what it needs to feed in return.
1. Series-shunt feedback (so called because it is in series with the input and shunts the output) will increase your input impedance and decrease your output impedance. This would be good for a voltage amplifier: voltage in, voltage out.
2. Shunt-shunt will decrease both your input and output impedances. This would make it a good transimpedance (transresistance) amplifier: current input, voltage output.
3. Shunt-series feedback would decrease the input impedance and increase the output impedance. This would make it a good current amplifier: current input, current output.
4. Series-series feedback would increase both the input impedance and the output impedance. This would make it a good transconductance amplifier: feed it with a voltage, and treat the ouput as a current source.
Hope that helps,
Erik Larson
Hi, Ed,
Edo said:
Yes, that is right. It is the influence of the feedback network that causes the impedance to change.
Here are the 4 basic feedback arrangements. Which one you would want to pick depends on what is feeding the circuit and what it needs to feed in return.
1. Series-shunt feedback (so called because it is in series with the input and shunts the output) will increase your input impedance and decrease your output impedance. This would be good for a voltage amplifier: voltage in, voltage out.
2. Shunt-shunt will decrease both your input and output impedances. This would make it a good transimpedance (transresistance) amplifier: current input, voltage output.
3. Shunt-series feedback would decrease the input impedance and increase the output impedance. This would make it a good current amplifier: current input, current output.
4. Series-series feedback would increase both the input impedance and the output impedance. This would make it a good transconductance amplifier: feed it with a voltage, and treat the ouput as a current source.
Hope that helps,
Erik Larson
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