A Grounded Constant Current Source with Improved Bandwidth

A grounded constant current source employing a single oper-j; >; -2y, = &g i (2kk+ 1). (A9 ationd amplifier is discus&. It is shown that improved bandwidth and k k I reduced slew rate limitations are obtained with this: circuit. Similarly the second product can be shown to be given by I: INTR~DUCDON fi xj’ 1 2k+l ( > N!(N+ l)! Circuit 1 of Fig. 1 is a commonly used single OP AMP j=k+ 1 X,‘-Xk’ k (IVk)!(N+ k+ l)! . (A3) voltage-controlled current source that has a grounded terminal. Combining (A2) and (A3) we finally obtain the solution It is listed in many texts and application notes, some of the more recent of which are [ l]-[5]. At low frequencies, this circuit acts as N!(N+ l)! Ak7N=(-1)k(2k+l)(N-k)!(N+k+1)! ’ 644) an ideal current source. However, at high frequencies, the load current tends toward zero if the OP AMP gain is characterized REFERENCES Manuscript received August 16, 1977; revised November 23, 1977. A. Budak is with the Electrical Engineering Department, Colorado State [I] 0. Herrmann, “On the approximation problem in nonrecursive digital University, Fort Collins, CO 80521. filter design,” IEEE :Trms. Circuit Theory, vol. CT-18, pp. 411-413, May R. Geiger is with the Electrical Engineering Department, Texas A&M 1971. University, College Station, TX 77843. 236 IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS, VOL. as-25, NO. 4, APRIL 1978 IL IL(O) cJ.s-Circuit I ---Circuit 2