Abstract: A system for testing a circuit which includes a receive section, a transmit section and a lock-out circuit for preventing the receive and transmit sections to be operative at the same time. The receive section has an input for receiving digital signals and an output for producing thereat analog signals corresponding to the digital signals at its input. The transmit section has an input for receiving analog signals and an output for producing thereat digital signals corresponding to the analog signals at its input. The lock-out circuit is coupled between the receive and transmit sections for disabling the transmit section while signals are being propagated in the receive section and for disabling the receive section while signals are being propagated in the transmit section.

Abstract: An integrated photodiode is formed by providing a silicon substrate with a deep recessed tub in excess of about 20 microns, forming an isolated p-n junction on the peripheral tub surfaces, and selectively epitaxially filling the tub with intrinsic silicon. A desired monolithic integrated circuit is fabricated outside the tub periphery using conventional VLSI techniques. A photodiode electrode structure within the tub periphery can be fabricated at the same time as other monolithic circuit components are formed.

Abstract: An integrated photodiode is formed by providing a silicon substrate with a deep recessed tub in excess of about 20 microns, forming an isolated p-n junction on the peripheral tub surfaces, and selectively epitaxially filling the tub with intrinsic silicon. A desired monolithic integrated circuit is fabricated outside the tub periphery using conventional VLSI techniques. A photodiode electrode structure within the tub periphery can be fabricated at the same time as other monolithic circuit components are formed.