Receiver for a differential data bus
View Patent ↗The invention relates to a receiver for a differential bus with a switch control logic ( 151 ), with two branches with resistive elements ( 7, 61 . . . 70, 8 and 5, 11 . . . 20, 6 ) and with switches ( 3, 80 ) for switching the resistive elements, in which the switch control logic sets the switches—in a first routine for determining the absolute level of signals on the bus by applying a common mode voltage to the bus, by comparing the voltage on a first resistive branch with a reference voltage, by selecting the correct switch settings, and by writing these settings to an internal storage device,—and in a second routine for minimizing the mismatch between the two resistive branches by applying a common mode voltage to the bus, by comparing the voltage of the second resistive branch with that of the already trimmed first resistive branch, by selecting the correct switch settings for the second branch, and by writing these settings to an internal storage device. The receiver therefore provides good balancing and common mode rejection.
1. Receiver for a differential data bus with two branches with resistive elements, which are coupled in a series arrangement in which the connections between the resistive elements are coupled to first terminals of switches wherein one of the switches of each branch is closed for receiving data from the bus and is coupled by its second terminal to comparators the receiver being provided with a switch control logic 51 which matches the resistive elements in two matching routines:
in a first routine for determining the absolute level of signals on the bus by applying a common mode voltage to the bus, by comparing the voltages at the switches in a first resistive branch consecutively with a reference voltage, by selecting the correct switch setting, at which the voltage at the activated switch has value closest to the reference voltage, and by writing this setting to an internal storage device,
and in a second routine for minimizing the mismatch between the two resistive branches by applying a common mode voltage to the bus, by comparing the voltages at the switches of the second resistive branch consecutively with that of the already trimmed first resistive branch, by selecting the correct switch setting for the second branch, at which the voltage at the activated switch has the value closest to the voltage of the switch of the first branch found in the first routine, and by writing this setting to an internal storage device.
2. Receiver as claimed in claim 1 , characterized in that the control logic sets the switches during the matching routine such that
in the first routine the switches of the first branch are set one after the other beginning with the switch closest to the bus lines and continuing with the next neighbor until the first switch is found, i.e. that switch whose voltage is lower than the reference voltage, this switch being selected as the correct one, and that
in the second routine the switches of the second branch are set one after the other beginning with the switch closest to the bus lines and continuing with the next neighbor until the first switch is found, i.e. that switch whose voltage is lower than the voltage of the switch of the first branch whose voltage was equal to the reference voltage in the first routine, this switch being selected as the correct one.
3. Receiver as claimed in claim 1 , characterized in that, for receiving data from the bus, the inputs of each of the two branches are coupled via a first resistors to two inverters whose outputs are coupled via second resistors to their inputs.
4. Receiver as claimed in claim 1 , characterized in that the differential bus is a data bus in a vehicle.
5. Receiver as claimed in claim 1 , characterized in that the differential bus is a data bus according to the FlexRay standard.