MOS switched-capacitor filters with reduced number of operational amplifiers

Using voltage inverter switches, exact analog sampled-data equivalents of Rs, Ls and Cs, as well as unit elements, can be designed with MOS capacitors and switches. Due to the underlying bilinear transformation, no limitation other than the Nyquist limit is imposed on the ratio of corner to sampling frequency. For an nth order filter, the number of voltage inverter switches is (n+1)/4 to (n+1)/2. A 3.4 kHz third-order Chebyshev low-pass CMOS circuit is described in detail. It uses only one voltage inverter switch implemented by a switched op amp integrator. The sampling frequency is 24 kHz, the dynamic range exceeds 70 dB and the chip area is 1.2 mm/SUP 2/. A CMOS voltage inverter switch, which has zero DC power and occupies only 0.09 mm/SUP 2/ is presented, whose dynamic range exceeds 85 dB. This allows low power switched capacitor filters without operational amplifiers and with a frequency capability approaching the megahertz range.     

Realization of transfer functions using differential-input operational amplifiers

A new active RC synthesis procedure for the transfer functions using signal-flow graphs is presented. Examples are given to illustrate the synthesis procedure.     

Resistive multiport scattering matrix realisation using operational amplifiers

A new structure realising the voltage-scattering matrix of resistive n-port networks using resistors and operational amplifiers is proposed. The effect of a finite gain-bandwidth product of operational amplifiers is discussed.     

Synthesis of RC networks containing operational amplifiers using flowgraph techniques

By using Coates's flowgraphs, a new approach to operational-amplifier?RC-network synthesis is given. The general biquadratic voltage transfer function is realised by this method. Furthermore, it is shown by an illustrative example that obtaining any other desirable transfer function directly from this realisation is possible.     

On the analysis of active networks containing voltage, operational, and differential-input operational amplifiers

A method of drawing by inspection the signal-flow graph of an active network containing voltage, operational, and differential-input operational amplifiers is given and it is shown that the network functions can easily be determined from the signal-flow graph.     

Synthesis of operational amplifiers

Operational amplifiers are specified from system considerations. A set of equations is evaluated giving the active part of the amplifier as a function of the specifications. The solution is claimed to be an optimal one with respect to circuit complexity. This statement is verified by an example.     

Multifunction active R filter with two operational amplifiers

A multifunction active R filter with two operational amplifiers, attractive for monolithic i.c. fabrication, is presented. It realises b.p., b.e. and l.p. transfer characteristics at three different output terminals. The resonant frequency of the b.p. characteristic can be controlled over a wide range with constant bandwidth and resonant gain.     

Equal-valued grounded-capacitor active RC realisation of all-pole transfer functions

An active RC structure with equal-valued grounded-capacitors and employing, at the most, two amplifiers is proposed for realising an all-pole transfer function of any order. Such a structure is attractive for integrated-circuit fabrication.     

A few more analog computer simulations of RC voltage transfer functions

A new synthesis procedure is described to obtain additional analog computer simulations of RC voltage transfer functions.     

Bilinear switched-capacitor ladder filter with reduced number of amplifiers

A novel technique is described for the design of bilinear switched-capacitor ladder filters with a reduced number of amplifiers.     

Technique for offset voltage cancellation in MOS operational amplifiers

A novel technique for the continuous-time removal of the input offset voltage in operational amplifiers is presented. This scheme converts a conventional op-amp into a similar differential-in/differential-out op-amp with zero differential input offset voltage. The nonzero common-mode input offset voltage can be isolated using a sampled-data time-averaging technique and minimised by negative feedback.     

Low voltage techniques [for micropower operational amplifiers]

A micropower operational amplifier is described that will operate from a total supply voltage of 1.1 V. The complementary class-B output can swing within 10 mV of the supplies or deliver /spl plusmn/20 mA with 0.4 V saturation. Common mode range includes V/SUP -/, facilitating single-supply operation. Otherwise, DC performance compares favourably with that of the LM108. An adjustable-output voltage reference is also presented that uses a new technique to eliminate the bow usually found in the temperature characteristics of the band-gap reference. Minimum supply is 1 V, and typical drift is 0.002 percent//spl deg/C.     

New switched capacitor ladder filter with reduced number of amplifiers

A new simple method for designing switched capacitor ladder filters with a reduced number of amplifiers is described. The main building blocks in this design method are SC immittance convertors and SC current sources.     

High-Q factor insensitive active RC network, similar to the tarmy-ghausi circuit but using single-ended operational amplifiers

A high Q, insensitive, active RC network, usable up to several megacycles, is described. It has similar properties to the circuit proposed by Tarmy and Ghausi, but uses operational amplifiers with single-ended output terminals. The circuit can be realised with only two amplifiers; using three, the two capacitors required can be earthed.     

Design formulas for biquad active filters using three operational amplifiers

A circuit configuration and its design formulas are presented for the realization of all the useful forms of a biquadratic voltage transfer function. The circuit employs three single-ended operational amplifiers, two capacitors, and at most eight resistors. With an additional resistor, it can realize any biquadratic voltage transfer function.     

Synthesis of actively compensated double-integrator filter without matched operational amplifiers

Actively compensated double-integrator filters proposed so far in the literature require matched operational amplifiers (OA's). Recently a double-integrator loop has been suggested to overcome this difficulty [1]. Even in this filter, the realized Qpis only free of error and is less sensitive to the gain-bandwidth (GB) products of the OA's. In this article, a new filter of this type is suggested which does not require matched OA's and is less sensitive to GB products by an order of magnitude in both realized Qpand ωp. Its superior performance will be brought out by both theoretical as well as experimental results.     

RC active bandpass filter synthesis using a voltage amplifier

An active RC filter employing a voltage amplifier as the active element has been chosen. The root sensitivity of the filter with respect to change in the gain of the amplifier has been calculated and minimized to establish a method of synthesis for achieving stability of center frequency and bandwidth.