Current Mirror - Current Mirror flac album

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 being "copied" can be, and sometimes is, a varying signal current. Conceptually, an ideal current mirror is simply an ideal inverting current amplifier that reverses the current direction as well. Or it can consist of a current-controlled current source (CCCS)

This is a current mirror, a device that uses the current in one half of the circuit to control the current flow in the other half. The current is the same in both halves. The switch on the left changes the current flow in the left half, which is mirrored in the right half. The switch on the right causes the resistor to be bypassed, but the current mirror ensures that the flow of current does not change. Q1's emitter-base junction acts like a diode

Conceptually, an ideal current mirror is simply an ideal current amplifier with a gain of -1. In Chapter 8 we explored the transistor and you should recall that the BJT device is a current amplifier of sorts (current controlled current source) in that the collector current is β times the base current. The problem with using this feature directly is that β is not a well controlled value from device to device and can vary with changes in temperature. Accurate current amplifiers are difficult to directly implement using conventional transistor amplifier configurations which are typically voltage.

Simple current mirror currents (MOSFET). The parameters for the transistors are W 900n, L 90n and VTN 0. The Widlar current source, a variation of the simple current mirror, was advanced by Bob Widlar in the mid 1960s. The only difference between the two circuits is the introduction of an emitter resistor. This additional component forces the currents in the two branches of the circuit to be unequal so this is why the circuit is called a source rather than a mirror.

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The input current to the mirror is labeled IREF. This current might come from a resistor connected to the positive rail or a current source realized with a transistor or another current mirror. The emitters of the two transistors are shown connected to ground. These can be connected to a dc voltage, . the negative supply rail. Figure 1: Basic current mirror. The simplest way to solve for the output current is to sum the currents at the node where IREF enters the mirror. Figure 3 shows the basic current mirror with a third transistor added. The collector of Q3 must be connected to a positive reference voltage, . the positive supply rail, which biases it in the active.

Current Mirror A MOS Transistor Biased by a Resistive Divider Sensitivity to VDD, resistor variations, and temperature. Basic Current Mirror Same length MUST be used for M1 and M2 A ratio of device dimensions. No dependence on process and temperature. Current Mirror Used to Bias a Differential Amplifier Reduce gm by reducing current rather than the aspect ratio. Reduce I(M3) and I(M4).

Constant current source(Current Mirror): A constant current source makes use of the fact that for a transistor in the active mode of operation, the collector current is relatively independent of the collector voltage. Current mirror and current sources: Constant current source(Current Mirror): A constant current source makes use of the fact that for a transistor in the active mode of operation, the collector current is relatively independent of the collector voltage. In the basic circuit shown in fig 1. Transistors Q1&Q2 are matched as the circuit is fabricated using IC technology

PMOS cascode current mirror is similar to NMOS version. Cascode amplifier with a cascode current mirror/active load. Gain of a Cascode amplifier with a cascode current mirror/active load. Output Resistance of a Cascode amplifier with a cascode current mirror/active load. Why Cascode Amplifiers are popular? Folded Cascode increases voltage overhead. gcariena,sAevth e−sm0. a5l(lg-smigrno)a2l, resistance of the current mirror to ≈ (gmro) ro o Cascode current mirror. Cascode Current mirror. Identical MOS: Same µCox and Vt, & (W, L)4 (W, L)2. o vGS1 vGS2 & vGS3 vGS4.