Basic Operation
The CDTA element with its schematic symbol in Fig 1 has a pair of low-impedance current inputs and p, n and an auxiliary terminal z, whose outgoing current is the difference of input currents. Here, output terminal currents are equal in magnitude, but flow in opposite directions, and the product of transconductance and the voltage at the z terminal gives their magnitudes. Therefore, this active element can be characterized with the following equations:
- ,
- ,
- ,
- .
where and is the external impedance connected to z terminal of the CDTA. CDTA can be thought as a combination of a current differencing unit followed by a dual-output operational transconductance amplifier, DO-OTA. Ideally, the OTA is assumed as an ideal voltage-controlled current source and can be described by, where Ix is output current, and denote non-inverting and inverting input voltage of the OTA, respectively. Note that gm is a function of the bias current. When this element is used in CDTA, one of its input terminals is grounded (e.g., ). With dual output availability, condition is assumed.
Read more about this topic: Current Differencing Transconductance Amplifier
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