Bjt transistor beta infinite meaning9/14/2023 ![]() In this voltage to current converter configuration, simple negative feedback across the transistor converts the voltage to current converter properties to an opposite logarithmic current to voltage converter. ![]() This is done by providing a voltage across the base-emitter junction of the BJT and the collector current is taken as an output. The first trick to use bipolar junction transistor as a current mirror circuit is to construct an exponential voltage to current converter using the transistor. Also the circuit implementation creates parasitic capacitance which results in frequency limitation.īipolar junction transistors are widely used for current mirroring. The current mirror circuit in the practical world has finite impedance which affects the current delivery process. Not only this, but theoretically in ideal current mirror circuits, the AC impedance is accepted as infinite, but this is not the case in real world scenario. ![]() This all affects the current mirror output. But in a real scenario they have noises, tolerance, ripples thus the output voltage varies. In the case of current mirror circuits, the voltage and current sources are ideal. But in the real world, the voltage also affects the constant current delivery process. Same as like the ideal voltage source, irrespective of the terminal voltage the current source can deliver or accept currents. In the real world, voltage sources like batteries, power supplies etc could not provide unlimited or infinite current to the loads. This is not the case in real-world voltage source. Therefore, we can connect any load resistance across the ideal voltage source and get a stable and fixed voltage every time. In ideal terminology, the voltage source will provide a fixed voltage constantly without being dependent on the load current. However, before understanding the limitations of current mirror circuits with respect of real-world applications, one needs to understand the voltage and current source and their ideal and actual behaviors.Ī voltage source is a device which is capable to provide fixed and stable voltage to the load. In the real world, there is nothing called perfect or ideal. The ideal circuit and the real circuit, these two are completely different. Limitations in Real Current Mirror Circuits A minimum voltage is required to keep the transistor in active mode, so the minimum voltage depends on the transistor specifications. A voltage range in which a Current Mirror Circuit can work is called compliance range, and the minimum to maximum supported voltage in this compliances range is called as compliance voltage. Thus, AC output resistance plays a major role in the stability of output current with respect to voltage changes.Ī proper working mirror circuit has a low voltage drop across the output. ![]() Resistance has a voltage-current relationship as per the ohms law. Therefore, for an ideal current amplifier, the current transfer ratio is an important parameter. An ideal current mirror circuit is an ideal current amplifier with the inverting configuration that can reverse the current direction. Thus the current mirror circuit is often referred to a Current Controlled Current Source or CCCS.Ĭharacteristic and Dependency of Current Mirror CircuitĪ current mirror circuit has lots of primary and secondary dependencies and that is the main concern to characterize current mirror circuit.Ī proper current mirror circuit can be characterized using three specifications.Ī current mirror circuit, mirror or copy the input current of one active device to the other active devices output. So by controlling the current in one device, the current in another device can also be controlled. If the current of the first device is changed, the mirrored current output of the other device will also change. In this, the current is flowing through one device can be copied into another device but in inverting form. In this technique, the circuit is designed in such a way that it copies the current through one active device to another active device with current control feature. The Current Mirror is a widely popular technique for monolithic IC design. ![]()
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