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A new current feedback amplifier (CFA) based dual-input differentiator (DID) design with grounded capacitor is presented; its time constant (
τ_{o}) is independently tunable by a single resistor. The proposed circuit yields a true DID function with ideal CFA devices. Analysis with nonideal devices having parasitic capacitance (
C_{p}) shows extremely low but finite phase error (
θ_{e}); suitable design
θ_{e} could be minimized significantly. The design is practically active-insensitive relative to port mismatch errors (
ε) of the active element. An allpass phase shifter circuit implementation is derived with slight modification of the differentiator. Satisfactory experimental results had been verified on typical wave processing and phase-selective filter design applications.

Differentiator and integrator functional blocks find a variety of applications in signal conditioning, wave pro- cessing and shaping, as process controller, phase compensator, and as pre-emphasis unit in radio engineering [

A new grounded capacitor single resistor tunable true dual-input differentiator design using the CFA-844 building block is presented in this work. The CFA device is essentially a current mode element with improved features compared to the ubiquitous VOA [

Analysis is carried out with both ideal and nonideal models of the device wherein the effects of the finite errors _{p}C_{p} arms appearing at the current source z-node are examined. As per databook [

The CFA based proposed DID topology is shown in

where

Note that no component matching constraint is needed to derive the transfer function in Equation (2) of the DID; time constant _{o}) while additional variation may also be conveniently achieved by ratio-k. With nonideal devices, Equation (1) modifies to

where_{1} input signal degeneration is negligible. The active sensitivity is

Re-examination of the circuit in

where

where

The differentiator quality fator (q) is estimated by writing

Equation (6) may be simplified to obtain a practical value of q after assuming

As an application of the differentiator, we now present the design of a first order allpass (AP) function realization. The differentiator circuit is slightly modified to derive the AP filter as shown in _{o}) with variable phase (ψ), given by

where

With

Effects of parasitic capacitances are examined next; re-analysis yields the modified transfer function as

where

sitic capacitances, the circuit provides a non-minimum phase function. Since

hence the phase components of numerator and denominator polynomials in Equation (9) are symmetrical. Writing

The phase response is therefore tunable in the nominal range and is seen to be practically unaffected by

Practical responses of both the DID and phase-selective AP filter had been measured using hardware circuit design employing readily available AD-844 type CFA device, and by PSPICE macromodel simulation; these are shown in _{o}; these are shown in

Next error estimation is carried out on the magnitude response of the DID for triangular to square wave conversion; these are listed in

A new CFA based dual-input high-quality active dual-input differentiator (DID) circuit realization scheme is presented. The advantages of the proposed design are true differentiation function implementation using a grounded capacitor while the time constant is tunable by a single resistor―features suitable for microminiaturization. The gain factor of the circuit may also be conveniently adjusted by a resistor ratio. CFA-based DID design is not readily available in the literature. Such dual-input differentiators are conveniently used as the error- subtractor cum rate controller in a process control loop. All the tunability features of the DID here are independently controllable without requiring any component matching constraint. Analysis with nonideal devices has been carried out which exhibits practically active-insensitive nature of the design. Investigation assuming finite device parasitic indicates certain phase deviation _{o}) adjustable by another resistor ratio. Test response indicates a phase deviation of

Square-wave | ||||||||
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R_{o} (KΩ) | ||||||||

C = 100 pF | Theoretical | Hardware | Simulation | Hardware | Simulation | |||

1.0 | 0.10 | 1.6 | 1.53 | 1.55 | 4.3 | 3.1 | ||

1.5 | 0.15 | 2.4 | 2.36 | 2.35 | 1.7 | 2.1 | ||

2.0 | 0.20 | 3.2 | 3.10 | 3.05 | 3.1 | 4.6 | ||

2.5 | 0.25 | 4.0 | 3.80 | 3.90 | 5.0 | 2.5 | ||

3.0 | 0.30 | 4.8 | 4.70 | 4.75 | 2.1 | 1.1 | ||

3.5 | 0.35 | 5.6 | 5.40 | 5.50 | 3.5 | 1.8 |

Anti-phase triangular wave input signals V_{1} = −V_{2} = 2 volt(pp) at 1 MHz with k = 1.