Fundamentals of Microelectronics II CH9 Cascode Stages in addition to Current Mirrors CH10

Fundamentals of Microelectronics II CH9 Cascode Stages in addition to Current Mirrors CH10 www.phwiki.com

Fundamentals of Microelectronics II CH9 Cascode Stages in addition to Current Mirrors CH10

Leanne,, Morning Show Co-Host has reference to this Academic Journal, PHwiki organized this Journal Fundamentals of Microelectronics II CH9 Cascode Stages in addition to Current Mirrors CH10 Differential Amplifiers CH11 Frequency Response CH12 Feedback Chapter 9 Cascode Stages in addition to Current Mirrors 9.1 Cascode Stage 9.2 Current Mirrors Boosted Output Impedances

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Bipolar Cascode Stage Maximum Bipolar Cascode Output Impedance The maximum output impedance of a bipolar cascode is bounded by the ever-present r between emitter in addition to ground of Q1. Example: Output Impedance Typically r is smaller than rO, so in general it is impossible to double the output impedance by degenerating Q2 with a resistor.

PNP Cascode Stage Another Interpretation of Bipolar Cascode Instead of treating cascode as Q2 degenerating Q1, we can also think of it as Q1 stacking on top of Q2 (current source) to boost Q2’s output impedance. False Cascodes When the emitter of Q1 is connected to the emitter of Q2, it’s no longer a cascode since Q2 becomes a diode-connected device instead of a current source.

MOS Cascode Stage Another Interpretation of MOS Cascode Similar to its bipolar counterpart, MOS cascode can be thought of as stacking a transistor on top of a current source. Unlike bipolar cascode, the output impedance is not limited by . PMOS Cascode Stage

Example: Parasitic Resistance RP will lower the output impedance, since its parallel combination with rO1 will always be lower than rO1. Short-Circuit Transconductance The short-circuit transconductance of a circuit measures its strength in converting input voltage to output current. Transconductance Example

Derivation of Voltage Gain By representing a linear circuit with its Norton equivalent, the relationship between Vout in addition to Vin can be expressed by the product of Gm in addition to Rout. Example: Voltage Gain Comparison between Bipolar Cascode in addition to CE Stage Since the output impedance of bipolar cascode is higher than that of the CE stage, we would expect its voltage gain to be higher as well.

Voltage Gain of Bipolar Cascode Amplifier Since rO is much larger than 1/gm, most of IC,Q1 flows into the diode-connected Q2. Using Rout as be as long as e, AV is easily calculated. Alternate View of Cascode Amplifier A bipolar cascode amplifier is also a CE stage in series with a CB stage. Practical Cascode Stage Since no current source can be ideal, the output impedance drops.

Improved Cascode Stage In order to preserve the high output impedance, a cascode PNP current source is used. MOS Cascode Amplifier Improved MOS Cascode Amplifier Similar to its bipolar counterpart, the output impedance of a MOS cascode amplifier can be improved by using a PMOS cascode current source.

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Temperature in addition to Supply Dependence of Bias Current Since VT, IS, n, in addition to VTH all depend on temperature, I1 as long as both bipolar in addition to MOS depends on temperature in addition to supply. Concept of Current Mirror The motivation behind a current mirror is to sense the current from a “golden current source” in addition to duplicate this “golden current” to other locations. Bipolar Current Mirror Circuitry The diode-connected QREF produces an output voltage V1 that as long as ces Icopy1 = IREF, if Q1 = QREF.

Bad Current Mirror Example I Without shorting the collector in addition to base of QREF together, there will not be a path as long as the base currents to flow, there as long as e, Icopy is zero. Bad Current Mirror Example II Although a path as long as base currents exists, this technique of biasing is no better than resistive divider. Multiple Copies of IREF Multiple copies of IREF can be generated at different locations by simply applying the idea of current mirror to more transistors.

Miller Compensation To save chip area, Miller multiplication of a smaller capacitance creates an equivalent effect.

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