Pull-up circuit
AssigneeNXP B.V.
InventorsRick Franciscus Jozef Stopel, Jerome Tjia
Life of this patent
Estimating the term…
Abstract
A pull-up circuit comprises an operational amplifier which forms part of a feedback circuit, acting to bring a pull-up circuit output equal to a reference voltage input. The pull-up circuit may form part of a USB transceiver for incorporation in a USB Device. When the supply voltage of the USB Device is sufficiently high, it is used to provide the required pull-up voltage, with the feedback circuit including the operational amplifier the USB Device is not high enough to provide the required pull-up voltage. In that case, the USB bus voltage is used to generate the reference voltage which is used as an input to the feedback circuit.
Claims20
A pull-up circuit, comprising:
- a pull-up circuit output;
- logic circuitry to generate an enable signal in response to a battery supply voltage;
- an active pull-up circuit block that, in response to a first logical value of the enable signal, brings the voltage on the pull-up circuit output to a reference voltage derived from an external voltage supply, the pull-up circuit block including
- a first input providing the reference voltage;
- a second input;
- an operational amplifier, having a reference voltage input connected to the first input thereof and an output, and
- a first transistor, controlled by the output of the operational amplifier, the first transistor having a first terminal connected to a first supply voltage input and having a second terminal connected to the pull-up circuit output and to the second input of the operational amplifier;
- and
- an alternative pull-up circuit block that, in response to a second logical value of the enable signal, brings the voltage on the pull-up circuit output to a reference voltage derived from the battery supply.
A pull-up circuit, comprising:
- an operational amplifier, having a reference voltage input connected to a first input thereof;
- and
- a first transistor, controlled by the output of the operational amplifier, the first transistor having a first terminal connected to a first supply voltage input and having a second terminal connected to a pull-up circuit output and to a second input of the operational amplifier;
- such that, when the operational amplifier is enabled, it acts to bring the voltage on the pull-up circuit output equal to the voltage on the reference voltage input, wherein the pull-up resistance comprises first and second resistors connected in parallel between the second supply voltage input and the pull-up circuit output when the pull-up circuit is in idle mode;
- a pull-up resistance, switchably connected between a second supply voltage input and the pull-up circuit output;
- and
- logic circuitry, for determining whether a voltage on the second supply voltage input is greater than a threshold voltage and,
- when it is determined that the voltage on the second supply voltage input is greater than the threshold voltage, for disabling the operational amplifier and for connecting the pull-up resistance between the second supply voltage input and the pull-up circuit output, and
- when it is determined that the voltage on the second supply voltage input is not greater than the threshold voltage, for enabling the operational amplifier and for disconnecting the pull-up resistance.
Dependencies are inferred from the claim text.