Current differencing transconductance

amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...

(CDTA) is a new active circuit element.

Properties

The CDTA is not free from

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...

input capacitances and it can operate in a wide

frequency range A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. The term may refer to a radio band or an interval of some other spectrum. The frequency range of a system is the range over which ...

due to current-mode operation. Some

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to ...

and current mode applications using this element have already been reported in literature, particularly from the area of frequency filtering: general higher-order filters, biquad circuits, all-pass sections, gyrators, simulation of grounded and floating inductances and LCR ladder structures. Other studies propose CDTA-based high-frequency oscillators. Nonlinear CDTA applications are also expected, particularly precise rectifiers, current-mode

Schmitt trigger In electronics, a Schmitt trigger is a comparator circuit with hysteresis implemented by applying positive feedback to the noninverting input of a comparator or differential amplifier. It is an active circuit which converts an analog input ...

s for measuring purposes and signal generation, current-mode multipliers, etc.

Basic operation

The CDTA element with its

schematic A schematic, or schematic diagram, is a designed representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the key information the ...

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 Transconductance (for transfer conductance), also infrequently called mutual conductance, is the electrical characteristic relating the current through the output of a device to the voltage across the input of a device. Conductance is the reciproc ...

(

gm\,

) and the voltage at the z terminal gives their magnitudes. Therefore, this active element can be characterized with the following equations: #

Vp=Vn=0\,

, #

Iz=Ip-In\,

, #

Ix+=gm.Vz\,

, #

Ix-=-gm.Vz\,

. where

Vz-=Iz.Zz\,

and

Zz\,

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

Ix=gm.(V+ - V-)\,

, where Ix is output current,

V+\,

and

V-\,

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.,

V-=0\;V\,

). With dual output availability,

Ix+=-Ix-\,

condition is assumed.

References

*Biolek, D.: CDTA – Building Block for Current- Mode Analog Signal Processing. In: Proceedings of the ECCTD’03, Kraków, Poland, Vol. III, (2003), 397-400 *Keskin A.Ü., Biolek, D., Hancioglu, E., Biolková, V: Current-mode KHN filter employing current differencing transconductance amplifiers, AEU - International Journal of Electronics and Communications, 60, (2006), 443-446 *Chen, H. Tsao, C. Chen,: Operational transresistance amplifier using CMOS technology. Electronic Letters., 28, 22 (1992), 2087–2088. {{DEFAULTSORT:Current Differencing Transconductance Amplifier Electronic amplifiers