Detail of the Current Conveyor Technology

     There are some users ask the detail of the Current Conveyor Technology , but cause by my poor English, I maybe can’t explain clear and detail.

      Nowdays, KRELL applied the Current Conveyor Technology in their Hi-End grade products and call “CAST” （Current  Audio  Signal  Transmission）.

       In Japan, there are some few  products cost million Yans based on the Current Conveyor Technology , they call  SATRI .

       In audio-gd products also applied Current Conveyor Technology  , for avoid the conflict , we call “ACSS” (Audio-GD Current Signal System) .

       In audio-gd ACSS technology, not only applied at analog field but also applied in digital signal transmit like audio-gd transports and digital convertor .

      The CAST, SATRI and ACSS are belong Current Conveyor Technology design but the detail circuit is different .

      The audio-gd ACSS products can work fine with the KRELL "CAST" and SATRI  products through the adapt  cable have proper plugs .

１，History

       The Current Conveyor technology mostly components are the current mirror. The Current Conveyor technology isn’t a new technology, at 1966 , professor K.C. Smith and A.S.Sedra  publish the concept  “current mode analogue circuits “  .

Two years later (1968), G. Wilson published the world-famous Wilson Current Mirror. At August ,1968, G. Wilson published “The Current Conveyor – A New Circuit Building Block” , and demo the first Current Conveyor circuit.

       Effect by the Ib of the transistors, the first generation Current Conveyor Circuit can not exact transmit the signal . In 1969, K.C. Smith and A.D. Sedra design the better exact  performance Current Conveyor circuit as the below.

          These two circuits both pertain to the first generation Current Conveyor Circuit. Even though designed at 60’ of 20 century, but in today, we still can see a lot popular OPA chips or discrete design applied the first generation Current Conveyor Circuit.  The first generation Current Conveyor Circuit. Can’t applied along, it must applied as a component in the finished design.

          Two years later, at 1970, Mr. Sedra design the second generation Current Conveyor Circuit.(CC II) . The second generation Current Conveyor Circuit.(CC II) can exact perform Voltage / Current conversion , so very quickly have agree in world , that time, a lot fanciers published a lot different designs based on the second generation Current Conveyor Circuit.(CC II) , but these design have not enough  frequency band and low slew rate, all can’t applied along.

            Until 1984, Brett Wilson published a new Current Conveyor Circuit ,  group by an OPA chip and a pair transistors Current Mirror, perform the voltage to current conversion , this design have up to 3MHz frequency band, THD low than -70DB. This design can output 10mA current while working at ±15VDC power supply and much improve than any early Current Conveyor Circuit. Design.

             At 1985, Mr. Normand published a most effective design group by full discrete transistors, it have better frequency band and low than -85DB THD, it can perform exact Voltage / Current conversion mutual.

             At 1995, Wadsworth design a Current Conveyor Circuit. and got the patent in USA . Later Wadia bought this patent technology and applied in their products, call "SC-1(Swift Current)"

           There are a lot designers do their best and spend several of ten years to develop the Current Conveyor technology from a component module grow up became a full design can applied in world.

2，Advantage of the Current Conveyor Technology

        We take the NFB-1 as the sample.
        In audio world , Simple and short signal transfer is best . The NFB-1 is a balanced DAC , built in ES9018 and discrete analogy parts .

        In some other ES9018 built in DAC design , ES9018 output signal have to through 3 step OPAs implement analogy signal process .

        The NFB-1 had different design , applies Non-feedback ACSS design. The ES9018 feed to the ACSS circuit by balanced model without any OPAs .

        The ACSS circuit naturally working in current model and have design difference current input , it can transfer the ES9018 current signal to output and implement the I/V conversion in current model in one ACSS amp . And this ACSS amp only have one current gain stage , the ES9018 output signal only through one stage can arrive the output stages .

        The shortest signal journey can reproduce the best detail and dynamic, and almost without sound coloration , It can show the real performance of the ES9018 .

3，Detail of the Current Conveyor Technology

The below diagram is the ACSS core of the NFB-1. This is a Current Conveyor Circuit (ACSS).
　

The NFB-1 is a balanced DAC, so it circuits built in four groups Current Conveyor circuit. Every Current Conveyor circuits have two inputs for connect to the ES9018 hot and cold balanced current signal output direct  .

The current output signal of ES9018 ,through ACSS circuit, output to XLR and RCA,  want to conversion to current signal,  a passive resistor (R1 in below diagram) can perform the conversion, but consider the source have different output impedance, so in NFB-1 have design four groups FET cascade buffer to keep the impedance as low and fixed .

The Current Conveyor  circuit group by the Wilson Current Mirrors . See below diagram.

If the resistors have same parameter, then  i3 = i4，

β mean the hFE of the transistor， β can’t be infinity，but if β is 300, i1 and i2 have low than  ０．００３％ zero，in engineering this is can be ignore , and we can choice the high β transistors to improve the performance reduce the zero .

In classis circuits, the signal have issue by transistors non-linear  . In Current Conveyor  circuit, the current through same type transistors, the transistors have same non-linear characteristic , so the output current signal have not any effect by the transistors non-linear, exact same as input signal .