1、New CCII Current Conveyor非：約翰魯濱遜Mar 27、2008abstract : offering higher bandwidth than its voltage-feedback counter part，The second-generation current conveyorr operationalIntroductionthe current conveyor has been around since the original design，or which can be regarded as an ideal transistor(CCI)，Wa

2、s initially PPPsCCI was then replaced by a more versatile second-generation device in 1970，The CCI。current conveyor designs have mainly been BJT due to their high trans conductance values compared to their CMOS counter parts . they are used a S currencethis means that the current fee D back operatio

3、nal amplifier is not restricted by the conventional gain band widths of a standard operational amplifiescurrent conveyors are used in high-frequency applications where The conventional operational amplifiers cannot be used，Because the conventionalsome applications where current conveyors are used to

4、day include Rf mixers，high-frequency precision rectifiers，and medical applicationsA Bipolar Conveyorthe diagram in figure 1 below shows a current conveyor implement using biblar devices。Figure 1。雙極CCI。from figure 1 it can be seen that the CCI conveyor can be modelled as an ideal transistor :Y being

5、the base/gateX being the emitter/sourcez軸the collector/drainthis type of circuit works well As a circuit with bjss，As the trans conductance and early voltages of bjss are much greater than that of CMOS devicestherefore，current conveyors workwell as source followwers。gain x/y is close to 1；z has a na

6、tural high-output impedance which cannot be mimicked by their CMOS counter parts。The CMOS Source FollowerAs previously expained，the major problem with a CMOS follower is the low GM and poor early voltage(1/lamb da)。this equtes to poor gain，Because the gain for a voltage follower heaviry relies on th

7、ese two parameters to be large。this can be observed in the equation below :Where GL is the load conductance，GDS is the drain source conductance and GM is the trans conductance of the CMOS device。a typical simulated gain with a TSMC 0.18m with a load of 1kgave a gain of 0.7。compared to the idal gain

8、of 1，this represents a 30% loss in output gain。Current Conveyor Source Followerone can use an unbuffered amplifier(figure 2a)to mimic a source follower with a gain of one . then this modification can be added to the basic diskFigure 2a。A simple source follower。figure 2a can be implement as shown bel

9、ow in figure 2b。Figure 2b。the CCI unbuffered source follower and implementation。from figure 2b it can be seen that output x is fed back to one of the long tail pairs of inputs(x)。the other input to the long tail pair is y，As input y changes the current through m1 . m2 differs As m3，and M4 is a curre

10、nt mirror。there is a current difference between m2 and M4。this imbalance is addressed by pulling current from，or to，The gate/source capitance cgs of device M5。until the output x matches that of y，The bandwidth limit is defined as The rate at which this transistor can be discharged and charged . thus

11、當(dāng)前轉(zhuǎn)換器(CCI) using an unbuffered amplifierFrom figure 2，the first part of the current conveyor(CCI)can be realized。to build The rest of The current conveyorr(CCI)，The current from output x simply has to be mirrored。to give zs output，see the example in figure 3。Figure 3。the current conveyor(CCI)using a

12、n unbuffered amplifier。the current from M5/M6 is simply mirrored by M7/M8，giving the output z(-)of the CCI。The output impedance of z can be improved by adding in a cascode to M7/M8 if necessary . one must be aware that to mimic The current successfullyThe gain of the CCII is simply:Converting from a

13、 CCI to a CCI-Taking the bias point Yb (figure 3)，simply add the extra connections as shown in figure 4。Figure 4。the current conveyor configured as a CCI-。From figure 4，if all transistor dimensions are the same and if Yb(the bias point from figure 3)is taken，Then a current 2i is generatedthis is mir

14、rored by M9 to give a current of 2i through M13。M12 provides a current of I and gives a c Urrent of-I through Z()，Thus giving a true CCI-output . there is a problem with this approachconequence，A 2i DC termneeds to be added to the output of z()to compensate for-I . figure 5 below shows the addition。Figure 5。the CCI-output with added DC bias。From Figure 5，Transistors m14 and M15 provide the appropriate current to compensate for the DC current taken by M13。(note that m14 and M15 must match M12)。make