PROGRAMMABLE VOLTAGE-MODE MULTIFUNCTION FILTER USING TWO CURRENT CONVEYORS AND ONE OPERATIONAL TRANSCONDUCTANCE

A new voltage-mode active-filter with single input and three outputs is presented. The parameters of the proposed filter are programmable and the filter uses grounded capacitors. The proposed circuit can simultaneously realize lowpass, highpass, and bandpass biquadratic filter functions and enjoys low temperature sensitivities.

However, because the auxiliary-bias-current is temperature-dependent, the parameters of the resulting active-filter structures suffer from relatively high temperature sensitivities.
It is the major intention of this paper to explore the feasibility of designing programmable multifunction filters with relatively low temperature sensitivities.Also it would be attractive for integration if a proposed implementation can be realized using grounded capacitors while enjoying high input impedance and independent control of the filter parameters.

PROPOSED CIRCUIT
The proposed circuit is shown in Fig. 1.Using the standard notation, the characteristics of the current conveyors can be described by i +/-i z, iy O, v x Vy for the CCII+_ and io gm (V+ V_) for the OTA, where gm IABc/2VT is the transconductance of the OTA, IABC is the auxiliary bias-current of the OTA, Vr kT/q is the thermal voltage, k is the Boltzman constant, T is the temperature, and v+ and v_ are the input voltages of the OTA.Routine analysis of the circuit yields the following transfer functions VBPF (gins Equation ( 1) corresponds to the transfer function of a bandpass filter, equation (2) corresponds to the transfer function of a lowpass filter, and equation (3) cor- responds to the transfer function of a highpass filter.
2 and too/Qo of the proposed From ( 1)-( 3), one can see that the parameters to voltage-mode filter realizations are given by  4) and ( 5), one can see that the parameters to o and too/Q can be adjusted by tuning the resistor R 1.Moreover, to can be adjusted by tuning gm without disturbing too/Qo.And since gm is a function of IABC this opens the way for current/voltage control of the parameter too- SENSITIVITY ANALYSIS By defining the passive sensitivity of a parameter F to the element of variation x by F dF x S 1 dx F it is easy to show that the sensitivity of the parameters too and too/Qo to the variations in passive elements are given by 0 S ('0 Similarly, the temperature-sensitivity of too can be expressed by 1 Thus, the too and too/Qo sensitivities to passive-elements and temperature are low.

SIMULATION RESULTS
To verify the theoretical analysis, the proposed circuit has been simulated using Pspice.The CCII_+ has been simulated using the simplified nonideal model shown in Fig. 2(a) [18] with Cy lpF,C z 1.5pF, Ry 20MI,R z 2M,Rxy 501,h h2 1.0.The OTA has been simulated using the simplified model shown in Fig. 2 with Rmp., 5MfI,Routpu, lOMfI,Co,tpu, ipF, gm lmA/V.The results obtained from the LPE HPF and BPE for different values of Qo, are shown in Fig. 3.These results are in good agreement with the theory presented.

CONCLUSION
In this paper a novel multifunction programmable voltage-mode active filter has been presented.The circuit uses two second-generation current conveyors and one operational transconductance amplifier (OTA) and can simultaneously realize the standard lowpass, highpass, and bandpass biquadratic filter sections.Values of too can be adjusted by tuning the transconductance of the OTA without disturbing too/Qo.This opens the way to programmable voltage(current)-control of the parameter to  1.OF,C: 1.OnF, C3 10nF, R1 1.0kll,R3 10.0kll,gm 5mA/V (b) Simulated bandpass, lowpass and highpass characteristics obtained from the circuit of Fig. 1 with Cl IOnF, C IOnF, C3 lnF,R 1.0kl,R 10.0kl,g lmA/V (c) Simulated bandpass, lowpass and highpass characteristics obtained from the circuit of Fig. 1 with C 10nF, C 0.1gF, C3 lnF, R 1.Okll,R 10.0kll,g,, lmA/V.

FIGURE 2 (
FIGURE 2 (a) Nonideal model for the current conveyor CCII+ and (b) Nonideal model for the OTA.