Abstract: In a commutation timing circuit for an electronically commutated motor (ECM), a solid state transconductance amplifier is used to convert the back emf appearing in an unenergized winding stage to a current. The current is then integrated in a capacitor, and at the correct voltage, a comparator generates the timing signal at the instant suitable for commutation of the winding stages. The transconductance amplifier has a differential input stage to which substantial degeneration has been provided to stabilize the transconductance. Subsequent stages of the amplifier, which include three current mirrors, exhibit substantially unity current gain. The circuit is provided with substantial degeneration to insure stability of the transconductance and with automatic self-nulling to correct imbalance of the amplifier.

Abstract: A tape recorder is described which is substantially fully integrated and which performs the required functions of a tape recorder in either the recording or playback mode. The tape recorder is readily converted from the record to the play mode of operation by simple switching means which operate to control selected current sources on the integrated circuit to activate or inactivate the functional blocks of the integrated circuit involved in the selected mode of operation. By the use of a temperature compensated reference in the emitter path of a differentially connected transistor pair to stabilize the current in two current mirrors not simultaneously operated, one may stabilize current sources associated with either mirror. The arrangement thus permits a highly economical method of mode control while at the same time preserving high temperature stability in all of the controlled functional elements.