What is meant by current mirror?
A current mirror is a circuit designed to copy a current through one active device by controlling the current in another active device of a circuit, keeping the output current constant regardless of loading. The current mirror is used to provide bias currents and active loads to circuits.
Why we are using PNP as current source?
Here the amplifying transistor is connected to ground; so, the active load should be a source whose output “pushes” a current into the collector/drain. Its output is the collector/drain; so its emitter has to be connected to +V. That is why this arrangement (kind of connection) requires a p-n-p (PMOS) transistor.
What is current mirror in BJT?
A current mirror is a transistor circuit that regulates the current through a load resistance, the regulation point is set by a simple resistor adjustment. Transistors in a current mirror circuit must be maintained at the same temperature for precise operation.
What is current mirror also draw its circuit and block diagram?
The basic circuit of the transistor current mirror is shown in the diagram below. It comprises two transistors, one of which has the base and collector connected and the other does not. The base connections of both transistors are then linked, as are the emitters which are also taken to ground.
What are the advantages of current mirror?
The advantages of a current mirror are:
- low input impedance makes the input current insensitive to the output impedance of the input source.
- high output impedance makes the output current insensitive to the impedance of the output load.
- inversion of sources to sinks or sinks to sources.
- accurate gain.
Can I use PNP instead of NPN?
Generally, the PNP transistor can replace NPN transistors in most electronic circuits, the only difference is the polarities of the voltages, and the directions of the current flow. PNP transistors can also be used as switching devices and an example of a PNP transistor switch is shown below.
What is difference between PNP and NPN transistor?
An NPN transistor has a piece of P-type silicon (the base) sandwiched between two pieces of N-type (the collector and emitter). In a PNP transistor, the type of the layers are reversed. NPN and PNP transistors have very similar schematic symbols. The only difference is the direction of the arrow on the emitter.
Why current mirror is used in op amp?
A current mirror is used to couple emitters in a differential input stage, to linearize the difference signals for them to share the currents in anti-phase. The stage normally has close thermal coupling to offset differences, and is a good basis for low distortion (best linearity) in op-amps and discrete amplifiers.
Why cascading is done in current mirror?
There are two major types- Basic / Active current mirror and Cascode current mirror. In the analysis of basic current mirrors, we have neglected channel length modulation. In order to suppress the effect of channel length modulation, a cascode current mirror can be used.
What is a current mirror circuit and why is it called so?
The current mirror circuit gains its name because it copies or mirrors the current flowing in one active device in another, keeping the output current constant regardless of loading. The current being mirrored can be a constant current, or it can be a varying signal dependent upon the requirement and hence the circuit.
Why do we use Wilson current mirror?
A Wilson current mirror or Wilson current source, named after George Wilson, is an improved mirror circuit configuration designed to provide a more constant current source or sink. It provides a much more accurate input to output current gain. The structure is shown in figure 11.9.
What is an example of a Q2 current mirror?
For example the collector load of Q4 collector, Ch 8 is a current mirror (Q2). For an example of a current mirror with multiple collector, outputs see Q13 in the model 741 op-amp, Ch 8. The Q13 current mirror outputs substitute for resistors as collector loads for Q15 and Q17.
Can multiple current mirrors be slaved from a single voltage source?
Multiple current mirrors may be slaved from a single (Q1 – Rbias) voltage source. Note that it is customary to draw the base voltage line right through the transistor symbols for multiple current mirrors! Or in the case of Q4 in the figure above, two current sources are associated with a single transistor symbol.
What is a current mirror circuit?
A current mirror is a transistor circuit that regulates the current through a load resistance, the regulation point is set by a simple resistor adjustment. Transistors in a current mirror circuit must be maintained at the same temperature for precise operation. When using discrete transistors, you may glue their cases together to do this.
What is the effect of temperature on PN junction current?
If both junction voltage and temperature are held constant, then the PN junction current will be constant. Following this rationale, if we were to hold the base-emitter voltage of a transistor constant, then its emitter current will be constant, given a constant temperature. Consider the example figure below