新型CCII电流传输器.doc

New CCII Current Conveyor By: John Robinson Mar 27, 2008 Abstract: Offering higher bandwidth than its voltage-feedback counterpart, the second-generation current conveyor operational amplifier (CCII) can be used in RF mixers, high-frequency precision rectifiers, and medical applications such as electrical impedance tomography. The conventional operational amplifiers cannot be used in the high-frequency applications due to their limited gain-bandwidth product.  Introduction The current conveyor has been around since the original design, or CCI (which can be regarded as an ideal transistor), was initially proposed by Smith and Sedra in 19681,2. CCI was then replaced by a more versatile second-generation device in 1970, the CCII3. Current conveyor designs have mainly been BJT due to their high transconductance values compared to their CMOS counterparts. They are used as current-feedback operational amplifiers such as the MAX4223 low-power amplifier, which features current feedback rather than the conventional voltage feedback used by standard operational amplifiers. This means that the current feedback operational amplifier is not restricted by the conventional gain bandwidths of a standard operational amplifier, and can offer a much higher bandwidth solution than its voltage-feedback counterpart.Current conveyors are used in high-frequency applications where the conventional operational amplifiers cannot be used, because the conventional designs are limited by their gain-bandwidth product. In theory, the current conveyor is only limited by the ft of the transistors used in its design. Some applications where current conveyors are used today include RF mixers, high-frequency precision rectifiers, and medical applications such as Electrical Impedance Tomography (EIT). A Bipolar Conveyor The diagram in Figure 1 below shows a current conveyor implemented using bipolar devices.Figure 1. A bipolar CCII.From Figure 1 it can be seen that the CCII conveyor can be