公开(公告)号：CA1159523A

公开(公告)日：1983-12-27

申请号：CA393980

申请日：1982-01-12

Applicant: MOTOROLA INC

Inventor： KELLEY STEPHEN H ,  ULMER RICHARD W ,  WHATLEY ROGER A

IPC: H03F3/34 ,  H03F1/30 ,  H03F1/14 ,  H03F1/34

Abstract: AUTO-ZEROING OPERATIONAL AMPLIFIER CIRCUIT A temperature stable bandgap voltage reference source utilizing bipolar transistors 12 and 14 biased at different emitter current densities is provided. Switched capacitors 28 and 34 are used to input the Vbe and the .DELTA.Vbe of the transistors 12 and 14 (PTC and NTC voltages, respectively,) into an operational amplifier 42 to provide a reference voltage VREF Proportional to the sum of he PTC and NTC voltages. Proper selection of the ratio of the switched capacitors 28 and 34 renders the reference voltage VREF substantially independent of temperature. In a modified form of the reference source 10, the reference amplifier 22 is implemented by an auto-zeroed operational amplifier 42 which uses switched capacitor techniques and an integrated capacitor 44 to achieve the auto-zeroing function.

公开(公告)号：CA1178338A

公开(公告)日：1984-11-20

申请号：CA393948

申请日：1982-01-12

Applicant: MOTOROLA INC

Inventor： ULMER RICHARD W ,  WHATLEY ROGER A

IPC: G05F1/56 ,  G05F3/30 ,  H03K3/26 ,  H03K17/60

Abstract: A temperature stable bandgap voltage reference source utilizing two substrate bipolar transistors biased at different emitter current densities is provided. Switched capacitors are used to input the Vbe and the .DELTA.Vbe of the transistors (NTC and PTC voltages, respectively) into an amplifier to provide a reference voltage VREF proportional to the weighted sum of the PTC and NTC voltages. Proper selection of the ratio of the switched capacitors renders the reference voltage VREF substantially independent of temperature. In a modified form of the reference, the reference amplifier is implemented by an auto-zeroed operational amplifier which uses switched capacitor techniques and an integrated capacitor to achieve the auto-zeroing function.

公开(公告)号：CA1172709A

公开(公告)日：1984-08-14

申请号：CA401184

申请日：1982-04-19

Applicant: MOTOROLA INC

Inventor： ALLGOOD ROBERT N ,  KELLEY STEPHEN H ,  ULMER RICHARD W ,  WURZBURG HENRY

IPC: H03F1/34 ,  H03F1/30 ,  H03H19/00 ,  H03M1/12

Abstract: A MULTIPLE FUNCTION OPERATIONAL AMPLIFIER CIRCUIT An operational amplifier capable of selectively performing a variety of circuit functions is provided. A single operational amplifier utilizes switched capacitors for sampling and holding an input signal, for establishing a low frequency pole, for applying the sample to an output capacitance to charge the capacitance and for comparing the input signal with a reference. The multi-function circuit provides a large savings in circuit area and permits versatility of circuit applications. One embodiment of the invention is to utilize a companding DAC having a capacitor array which may be used as the output capacitance of the operational amplifier circuit. The DAC provided utilizes an R ladder DAC coupled directly to a C DAC and has a switching structure that is simpler than comparable prior art circuits, The DAC is asynchronous and has programmable Aand Mu-255 law PCM conversion capability. Coupled directly to the C DAC is an operational amplifier receive filter circuit which utilizes the C DAC as an input capacitor thereby eliminating the need for a buffer amplifier and allowing the DAC to be used for both analog to digital and digital to analog conversion.