VERSATILE ACTIVE BIQUAD BASED ON DUAL-OUTPUT SECOND-GENERATION

A universal active biquad based on the dual-output second-generation current-conveyor (CCII±) is presented. The circuit uses only six CCII± and can, simultaneously, support three mixed-mode transfer functions and five current-mode transfer functions. The circuit uses grounded resistors and capacitors and enjoys independent grounded-element control of the filter parameters.


INTRODUCTION
In a recent publication, Sun and Fidler  [1], present a versatile active biquad using seven second-generation current-conveyors.The circuit can simultaneously realize four different filter characteristics; one output current and three output voltages.The output current can realize low-pass, highpass, bandpass and bandstop characteristics.Realization of allpass characteristics is feasible, but requires replacing a plus-type second-generation current-conveyor (CCII + ) by a minus- type second-generation current-conveyor (CCII-).The output vol- tages can simultaneously realize lowpass, highpass and bandpass characteristics.
Here we propose to use the dual-output CCII+; its symbolic representation and matrix equation are shown in Figure 1, for realizing single-input multiple-output active biquad.The proposed circuit can simultaneously support eight different current-mode and mixed-mode transfer functions, while using only six dual-output CCII+.

Proposed Circuit
The proposed circuit, using only CCII+, is as shown in Figure 2.
Compared to the circuit proposed by Sun and Fidler [1], the proposed circuit have the following advantages: 1) Use of fewer number of active elements; only six CCII+ rather than seven as proposed in [1].2) Simultaneous support of eight different transfer functions; three mixed-mode and five current-mode.The circuit proposed in [1] can simultaneously support only three voltage-mode and one current- mode transfer functions.
From (1-9) it can be seen that the parameters coo and coo/Qo From (10) and (11) it can be seen that the paramter COo can be controlled by adjusting the resistance R (1/G) and/or the resistance Rbo=(1/Gbo) and/or the capacitor C1 without disturbing the parameter COo/Qo.It can also be seen that the parameter COo/Qo can be controlled by adjusting the resistance Rb=(1/Gb) without disturbing the parameter COo.Thus the circuit enjoys independent grounded-element control of the parameters COo and COo/Qo.However, for the allpass realisaiton, and because of the required matching conditions, the parameter COo can be controlled only by adjusting the capacitance C without disturbing the parameter COo/Qo.The parameter COo/Qo cannot be controlled without disturbing the parameter COo.

CONCLUSION
A new active biquad based on dual-output second-generation current conveyors has been presented.The proposed circuit uses only six CCII+ and can simultaneously support eight different filter transfer function.Compared to the circuit proposed in [1], the present circuit uses less number of active components and can simultaneously provide larger number of different transfer functions while using grounded capacitors and resistors.Similar to the circuit proposed in [1], the present circuit enjoys independent grounded-element control of the filter parameters.These features make the circuit more attractive for integration. FIGURE