The first stage is a pMOS differential pair with nMOS current mirrors. Department of EECS University of California, Berkeley EECS 105Fall 2003, Lecture 17 Prof. A. Niknejad Common Gate Amplifier The PMOS transistor MP with a constant VGSbehaves as a constant current source. To minimize errors related to the voltage drop on bounding wires from the source current of the major device, two separate terminals, one for a current mirror current return (SR) and Common gate amplifier. The current through R L is independent on the value of R L (provided that the MOSFET remains in saturation). Working of PMOS When the gate terminal is given a negative potential at VGG than the drain source voltage VDD, then due to the P+ regions present, the hole current is increased through the diffused P channel and the PMOS works in Enhancement Mode. An implementation of current steering circuit to bias several transistors in an IC. current source becomes open circuit . AD7719 ADC has a similar current source setup, with the maximum current at 400 μA (see Figure 2). o No signal: effectively open circuit (Careful about current mirrors as they are NOT “ideal” current sources, channel width modulation was ignored!) Common source amplifier with Ideal current source as load and PMOS current source as load are explained. Unlike (3), however, the drain current is now no longer independent of the source-drain voltage due to channel length modulation. Figure 1(b) shows the ideal current source implemented by PMOS with constant gate to source voltage. Figure shows the current sink circuit based on NMOS transistor. cs-7 small signal : r out r out r out r o 1 λ ⋅ i out ==-----i out = 10µa λ = 0.01 r out = 10mΩ nmos current sink pmos current source r v dd eecs140 analog circuit design lectures on current sources cs-8 … The simple current mirror can be obtained from the one transistor current source by using a second transistor in diode connection that generates the necessary gate-source voltage of the transistor in the output ... NMOS and PMOS implementations of a simple current mirror . The current equation of the transistor MP in saturated case is given by: ... Small-signal model for PMOS and for rest of circuit. In Units 5.1 and 5.2 we discuss various aspects of the common-source stage with grounded source, in Unit 5.3 we take up circuit-linearity considerations, and in Unit 5.4 we cover the basics of the dual-power-supply amplifier. One can realize multiple current sources for biasing applications from the same structure using PMOS devices with different ( W / L ) ratios: Note that V OUTk needs to be always small enough such that Mk remains in saturation 10/22/2004 Example PMOS Circuit Analysis.doc 3/8 Jim Stiles The Univ. Shown in the diagram are reasonable widths in 0.18um technology (length all made 0.3um). Gain of a Cascode amplifier with a cascode current mirror/active load F. Najmabadi, ECE102, Fall 2012 (14/17) eecs140 analog circuit design lectures on current sources simple source (cont.) There are wide applications of Current Mirror Circuit in the field of integrated circuit manufacturing. The first thing we should do is to give power to the circuit, so that it can operate. Then, ( )^2(1 ) 2 1 ISD = µpCox VSG −Vtp +VSDλ From this equation it is evident that ISD is a function of VSG, VSD, and VSB, where VSB appears due to the threshold voltage when we have to … At first current-mirror circuit 102 having a current gain G11 incorporates a first PMOS transistor 104 which passes a first current I11 from a power source voltage V DD and a second PMOS transistor 106 which passes a second current I12 multiplied by current gain G11 to first current I11. The current source circuit that we will build with an op amp and MOSFET is shown below. Current independent of voltage for ideal source . We’ve determined all the important stuff (i.e., V • Trade-off resolved using current-source pull-up: use PMOS as current source. This is Think about what this means—this device is a current source! Vi Vo VDD VG2 VDD Vo Vi M1 M1 M2 (a) (b) VG1 VG1 F 1 An P-Channel MOSFET is made up of a P channel, which is a channel composed of a majority of hole current carriers. The reference current source is created using the current mirror circuit. The breadboard circuit of the circuit above is shown below. Reasonable sizes for the lengths are usually 1.5 to 10 times of the Current Sources When in saturation region, a MOSFET behaves as a current source. By using this technique, multiple reference points can be created from a single source. The condition to operate the transistor as a current sink is that, the voltage V B should be applied with fixed biasing voltage and the drain voltage applied to the transistor should be less than the gate overdrive voltage (V GS – V TH ). Figure 20.29 Biasing of the cascode current source and its operation. Exercise: Draw the circuit for a PMOS cascode with a cascode current mirror (cascode current mirror would be made of NMOS). Similarly, two current sources are available. PMOS Current Mirror: • NMOS current source sinks current to ground • PMOS current source sources current from positive supply. DC Operation The voltage on the gate of M4 in Fig. The simu- low frequency noise from the bias current source was an impor- lated phase noise values of the TITO-VCO using a PMOS tran- tant contributor to the phase noise, the tail current source was sistor were 10 and 5 dB lower than those observed using the removed. pMOS I-V • All dopings and voltages are inverted for pMOS • Mobility m p is determined by holes – Typically 2-3x lower than that of electrons m n – 120 cm2/V*s in AMI 0.6 mm process • Thus pMOS must be wider to provide same current – In this class, assume m n / m p = 2 to 3 Both current sources are 200 μA and can be controlled in a similar manner to the AD7794 ADC: one or both currents can be sent to the one output pin. FET Current Sources Figure 1(a) shows two FET current sources, one which uses an n-channel depletion … 2. A PMOS current mirror. Figure 1(a) shows a common gate amplifier with ideal current source load. Second stage is a common-source amplifier. Current Source Supply Solution: Use a current source! linear region and saturation region.. of EECS Note what we have quickly determined—the numeric value of drain current (I D=1.0 mA) and the voltage drain-to-source (V DS =-1.0) Moreover, we have determined the value V GS in terms of unknown voltage V GG0 (5 V GS GG=V.− ). quadratic) dependence on the source-gate voltage. Small Signal Analysis of a PMOS transistor Consider the following PMOS transistor to be in saturation. I-V Characteristics of PMOS Transistor : In order to obtain the relationship between the drain to source current (I DS) and its terminal voltages we divide characteristics in two regions of operation i.e. The current mirror is created as a part of the major MOSFET structure with common drain (D) and gate (G) terminals and separated source terminals (S and CS). This section covers other current sources that are often seen. Both amplifiers are based on the PMOS, as in the projects. 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Due to channel length modulation circuit for a PMOS cascode with a current-source bias ( dual power )! Single source the reference current source is created using the current source current... Rest of circuit section covers other current sources that are often seen reference points can created!

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