PROGRAMMABLE CURRENT-CONVEYOR-BASED VOLTAGE-MODE FILTER WITH SINGLE INPUT AND FIVE OUTPUTS

At present, there is a growing interest in designing universal current-mode and voltage-mode active filters. Thus, a number of circuit realizations, for universal current-mode and voltage-mode filters, using current-conveyors or operationaltransconductance-amplifiers (OTAs) were proposed [1-17]. A critical study shows that while some of the proposed circuits use grounded resistors and capacitors [1-6,11-13], other circuits use floating resistors and/or capacitors [7-10,15-17]. The majority of the proposed circuits can realize all the basic biquadratic filter functions, that is, lowpass, highpass, bandpass, allpass and notch. However, in most of the circuits, this can not be achieved simultaneously. Moreover, while the filter parameters in current-conveyor-based circuits are not programmable, in OTAbased circuits these prameters are programmable. This is attributed to the dependence of the OTA-transconductance (gm) on the auxiliary bias-current IABC. However, because the auxiliary-bias-current is temperature-dependent, the parameters of the resulting active-filter structures suffer from relatively high temperature sensitivities. As an illustrative example, consider the circuit proposed by Chang [1]. While the circuit can simultaneously realize lowpass, highpass, and bandpass functions, to obtain an allpass function it is necessary to connect the three output currents. Similarly, to obtain a notch function it is necessary to connect the highpass and the lowpass output currents. Thus, the five basic filter functions can not be realized simultaneously. While the circuit has the advantage of using grounded resistors and capacitors, its parameters are not programmable. It is the major intention of this paper to explore the feasibility of designing programmable universal filters with relatively low temperature sensitivities. Also, it would be attractive for integration if a proposed implementation can be realized using grounded resistors and capacitors while enjoying high input impedance and independent control of the filter parameters.

However, because the auxiliary-bias-current is temperature-dependent, the parameters of the resulting active-filter structures suffer from relatively high temperature sensitivities.
As an illustrative example, consider the circuit proposed by Chang [1].While the circuit can simultaneously realize lowpass, highpass, and bandpass functions, to obtain an allpass function it is necessary to connect the three output currents.Similarly, to obtain a notch function it is necessary to connect the highpass and the lowpass output currents.Thus, the five basic filter functions can not be realized simultaneously.While the circuit has the advantage of using grounded resistors and capacitors, its parameters are not programmable.
It is the major intention of this paper to explore the feasibility of designing programmable universal filters with relatively low temperature sensitivities.Also, it would be attractive for integration if a proposed implementation can be realized using grounded resistors and 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 ix +iz,iy O, Vx 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  Equation ( 1) corresponds to the transfer function of a bandpass filter, equation (2) corresponds to the transfer function of a lowpass filter, equation (3) corresponds to the transfer function of a highpass filter, equation ( 4) corresponds to the transfer function of a notch filter, and equation ( 5) corresponds to the transfer function of an allpass filter.
From ( 1)-( 5), one can see that the parameters to 2 and too/Qo of the proposed O voltage-mode filter realizations are given by 2._.gm/CCzR (6) too and too 1/ClR (7) Qo From ( 6) and ( 7), one can see that the parameters too and too/Qo can be adjusted by tuning the grounded resistor R1.Moreover, too can be adjusted by tuning gm without disturbing too/Qo.And since gm is a function of IABO 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 xi by dF x dxi F it is easy to show that the sensitivity of the parameters to o and too/Qo to the variations in passive elements are given by Similarly, the temperature-sensitivity of too can be expressed by 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 20Mf,R z 2M[,Rxy 50-, h h 2 1.0.The OTA has been simulated using the simplified model shown in Fig. 2
With R 1 lkf,R 3 R4 Rs R6 R7 Ra R9 10kf,C1 C2 lOnF, Ca lnF, the results obtained from the LPE HPE BPE APF and the notch filter are shown in Fig. 3.These results are in good agreement with the theory presented.

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