Abstract: A programmable-threshold power supply selector has two power-supply inputs VDD1 and VDD2. The higher of these two voltages is pre-selected as a common supply that powers all transistors and circuitry in the programmable-threshold power supply selector, including substrates under transistors. An open-loop decision circuit is very stable since it uses no feedback. A tunable voltage divider divides VDD1 by a programmable divisor. The divided VDD1 is compared to a reference voltage to generate switch-control signals. The switch-control signals drive the gates of p-channel switch transistors that connect either VDD1 or VDD2 to an output supply voltage. The different programmable divisor values effectively cause VDD1 to be compared to a programmable threshold voltage VTH. The switch transistors switch the output supply voltage to VDD2 only when VDD1 falls below VTH. The output supply voltage remains at VDD1 even when VDD1 falls below VDD2, eliminating unnecessary power switching.

Abstract: An integrator in a duty-cycle adjustment circuit has an adjustable charging current provided by a switched current-source array in response to configuration signals from the calibration logic. The integrator's ramp voltage is compared to a threshold voltage by a comparator to generate an output clock. A tunable voltage reference generates a reference voltage that can be tuned by configuration signals from the calibration logic. The reference voltage is divided by a tunable voltage divider, which selects different fractions of the reference voltage for use as the threshold voltage. During calibration, calibration logic repeatedly raises the reference voltage or reduces the charging current from the switched current-source array until a peak voltage of the ramp voltage equals the reference voltage, when a zero duty onset detector detects that the output clock has stopped pulsing. The configuration signals at the zero duty onset condition are stored and used for normal operation.

Abstract: A programmable-threshold power supply selector has two power-supply inputs VDD1 and VDD2. The higher of these two voltages is pre-selected as a common supply that powers all transistors and circuitry in the programmable-threshold power supply selector, including substrates under transistors. An open-loop decision circuit is very stable since it uses no feedback. A tunable voltage divider divides VDD1 by a programmable divisor. The divided VDD1 is compared to a reference voltage to generate switch-control signals. The switch-control signals drive the gates of p-channel switch transistors that connect either VDD1 or VDD2 to an output supply voltage. The different programmable divisor values effectively cause VDD1 to be compared to a programmable threshold voltage VTH. The switch transistors switch the output supply voltage to VDD2 only when VDD1 falls below VTH. The output supply voltage remains at VDD1 even when VDD1 falls below VDD2, eliminating unnecessary power switching.