A family of operational amplifiers are described which utilize only MOSFET transistors as the active devices. These operational amplifiers exhibit an infinite input impedance and zero input offset and bias currents. The circuits are capable of operating over a wide range of DC supply voltages at extremely low DC current drain. An operational amplifier is shown which operates from a single positive DC supply voltage and which handles a wide range of input common mode voltage swings including some negative common mode voltages. Another operational amplifier is shown which operates from a combination of a single positive and a single negative supply voltage and which handles a wide range of positive and negative input common mode voltage swings.
A detection circuit particularly adapted as a smoke detector employs a minimum number of components by a CMOS integrated circuit which receives directly the output of a smoke detector on one of the inputs of an input comparator circuit which provides static input protection and a high input impedance by employing thick oxide layer over the gates of the comparator transistors. The CMOS chip also directly supplies operating current for a mechanical or piezoelectric horn. Further features include a clocked low voltage alarm; a buffer stage to permit the interconnection of a number of different detector circuits in common to a single input/output lead; and a visual LED indicator to indicate that the circuit is operating and to provide a visual indication any time the alarm condition for the circuit has been actuated.
An operational amplifier wherein each of the active elements is comprised of complimentary coupled pairs of insulated gate type field effect transistors is provided. A first active stage and a second active stage are coupled together to perform a predetermined transfer function. Each active element in the first and second stages are insulated gate type field effect transistors that are coupled in complementary pairs with the first stage and second stage being coupled to define mirror pairs.
An operational amplifier is provided with a differential amplifier constructed by MOS transistors and a linear amplifier constructed by MOS transistors and coupled with the differential amplifier. The differential amplifier is supplied with first and second inputs. The output of the operational amplifier is derived from the output of the linear amplifier. A stabilizing circuit, which is coupled with the differential and linear amplifiers, stabilizes the output of the operational amplifier against a variation of the input DC levels to the differential amplifier.
A detection circuit particularly adapted as a smoke detector employes a minimum number of components by a CMOS integrated circuit which receives directly the output of a smoke detector on one of the inputs of an input comparator circuit which provides static input protection and a high input impedence by employing thick oxide layer over the gates of the comparator transistors. The CMOS chip also directly supplies operating current for a mechanical or piezoelectric horn. Further features include a clocked low voltage alarm; a buffer stage to permit the interconnection of a number of different detector circuits in common to a single input/output lead; and a visual LED indicator to indicate that the circuit is operating and to provide a visual indication any time the alarm condition for the circuit has been actuated.
A circuit is described which uses a thick gate oxide device in the input stage and a thin gate oxide device in a second stage that is connected to the input stage. The input stage thick gate oxide device provides a low input gate leakage current. The thin gate oxide device in the second stage has high performance characteristics due to the use of the thin gate oxide device. The circuit thereby has high performance characteristics and low input gate leakage current. In various applications, the circuit may be, for example, an amplifier, a differential amplifier, a variable gain differential amplifier, or an operational amplifier in a sample and hold circuit. A guideline is provided where the thick gate oxide layer is about 1.5.times. the thickness of the thin gate oxide layer. Also, a design to control the circuit's common mode voltage using common mode voltage feedback is described.
