Wanlop Surakampontorn

Low-Voltage Current Differencing Buffered Amplifier Using Only NMOS Transistors

A circuit realization of a current differencing buffered amplifier (CDBA) in low-voltage operation is presented. The scheme is through the modification of a low-input resistance CCII+ and the proposed CDBA can operate with the minimum supply voltage of plusmn1.25 V. In order that the signal path consists of only NMOS transistors, a negative current mirror using NMOS transistors is employed. With standard 0.5-mum CMOS process parameters, PSPICE simulation results show that the proposed CDBA provides the terminal resistances of rn = rp = rw= 13 Omega, rz = 290 kOmega, and f-3db cong 3 500 MHz.

Cascadable Current-Controlled Current-Mode Multifunction Filter Using CDTAs

The cascadable current-controlled current-mode multifunction filter with three inputs and one output using current differencing transconductance amplifiers (CDTAs) as active components is presented. The proposed configuration comprising only three CDTAs and two grounded capacitors provides low-input and high-output impedances, which is advantageous from an integration point of view and is important for easy cascading in the current-mode operations. By properly joining the input and output terminals, the circuit can simultaneously realize all the standard filter functions, namely lowpass (LP), bandpass (BP), highpass (HP), bandstop (BS) and allpass (AP), without any component matching conditions. The natural angular frequency (omegao) and the bandwidth (omegao/IQ) of the proposed filters can be electronically controlled, thanks to the tunability properties of the CDTAs. All the passive and active sensitivities are low. SPICE simulation results are included to confirm the theory.