endobj A current mirror circuit is one where the output current is forced to be equal to input current and can be designed either with identical BJT or FET. – The analysis and design of MOS and BJT differential amplifiers. In this case (differential input signal), they are equal and opposite. The voltage across the base-emitter is constant depending on the current flowing through the diode. Use Fairchild 2N3904 for all transistors in the design. x�����q\�^�8�i�);���W���z�b��&3�}��M������!�o�[�[�Q��*�T�_����#�(���I7���!�xt��I�/�s�\ q�. The 6. NTRODUCTION The typical BJT differential pair amplifier consists of a pair of transistors coupled at the emitters to a current source, having equal resistances in each collector and equal but opposite, signal sources in each base. A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. The amplifier has several variations on this basic configuration. The current mirror circuit in the practical world has finite impedance which affects the current delivery process. Set 11 - MOSFET multi-stage amplifier problems. Using this equation and equation (11.9), the collector current I C1 and I C2 of the transistor are separately derived shown in equation (11.10) and (11.11). Use Fairchild 2N3904 for all transistors in the design. amplifier bjt differential frequency-response asked 8 mins ago A proper working mirror circuit has a low voltage drop across the output. Replace RE with Current Mirror that draws ~ 4 mA. In the above formulas, KP is a transistor technology related constant, W/L is the ratio of Width and Length and λ is used for the modulation constant of channel length. An amp meter is connected on both input and output current side. amplifier. In the circuit shown to the right, we have replaced R E with a current mirror.As a result, the total emitter current I E is now much less dependent on emitter voltage, V E.There will still be some variation due to the internal resistance of Q4, but its effect will be reduced. In the active mode operation, the transistor collector current can be calculated by multiplying the base current with the ratio of β. Analog Circuit Design (New 2019) Professor Ali Hajimiri California Institute of Technology (Caltech) http://chic.caltech.edu/hajimiri/ © Copyright, Ali Hajimiri Connect with us on social media and stay updated with latest news, articles and projects! Because MOSFETs usually have lower output resistances than BJTs, this circuit often causes lower gains than its BJT counterpart. The same gate to source voltage is reflected across the M2. >> In the previous image, a forward biased diode is used in parallel of the base-emitter junction which is providing constant voltage to the transistor. Simplest bipolar current mirror within a differential amplifier. Subscribe below to receive most popular news, articles and DIY projects from Circuit Digest, The CR01005 chip resistor features a three-layer termination process with a nickel barrier. Instead of the programming resistor, a potentiometer is used to control the current flow in the live simulation. Be- cause Q3 is connected as a diode, it has a low impedance to the power supply. The compliance voltage, where the VDG = 0 and the current mirror behavior still works in the lowest output voltage, can be calculated like this: VCV = VT ln ((IC / IS) +1)) Where VT represents thermal voltage and IS is the scale current. However, the voltage swing in fully-differential version is twice that of the Current Mirror— Differential Amplifier •Review – Common base amplifier • Small-signal equivalent circuit • Small-signal analysis • Reading – Chapter 6.1 – 6.3 MOS/BJT Current mirror – Chapter 7.1 – 7.5 MOS/BJT Differential amp Current sources • How to make a reference current source? However, the voltage swing in fully-differential version is twice that of the Within the circuit, a third transistor is introduced. This same thing is created for the 2N6660 MOSFETs. In the real world, voltage sources like batteries, power supplies etc could not provide unlimited or infinite current to the loads. Simulating Differential Amplifiers 4 ... • BJT Current Mirror Basics • MOS Current Mirrors Basics 35. Differential Amplifier with Active Loads Active load basics PNP BJT current mirror ... Due to imbalance created by active load current mirror, only single-ended output is available from common collector of Q2 and Q4. 2. In ideal terminology, the voltage source will provide a fixed voltage constantly without being dependent on the load current. So, the formula can be written using the below function. It may have either one output or a pair of outputs where the signal of interest is the voltage difference between the two outputs. In the image, the input current is provided by the bias resistor. 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. Thus, AC output resistance plays a major role in the stability of output current with respect to voltage changes. p8.49 (calculate and simulate): BJT differential amplifier with current mirror. �d�H�E��f/�P�VzQam�:"����E����#G��T�=��*�$)�����T���OA��߃S�������?�|��q`՛�ll��աq�)E݁�^ �)��m�Ddi!0��Śs�����b�\�����e-� ��v�\��Ɵcx��bʹh[y�σ������S���Z�I��g�2 �%/@ 9̼�\�v���o M�Eϧm��/H%�ǉ�� �..}��Ӡj�m�4�da�mG���\��g� Notice the power dissipation and slew rate is the same. This is not the case in real-world voltage source. Rail=+/- 5V. Before understanding how the circuit works it is essential to understand the transistor operating characteristics. The compliance voltage, where the VDG = 0 and the output MOSFET resistance is still high, current mirror behaviour still works in the lowest output voltage. we assume VA→∞. CH 9 Cascode Stages and Current Mirrors 36 Temperature and Supply Dependence of Bias The reason given is that the current mirror has a very high output impedance and behaves like an active load. 2) You can use the same chip for the diff pair and the basic current mirror. There are wide applications of Current Mirror Circuit in the field of integrated circuit manufacturing. fig. The current mirror circuits are based on the principle that, if the gate to source voltage of two identical MOSFETs are equal then the drain current flowing through them is equal. 0. – The analysis and design of MOS and BJT differential amplifiers. The circuit consists of an input diﬀamp and four Wilson current mirrors. In the real world, there is nothing called perfect or ideal. A current mirror circuit, mirror or copy the input current of one active device to the other active devices output. 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