Patent ID: 6191816
Filing Date: 2001-02-20
Classification: H04N

Abstract:
An interface circuit that is capable of receiving a pseudo-periodical input signal, each pseudo-period of which comprises at least a first and a second consecutive time interval, the input signal having a reference level during the first time interval and a video level during the second time interval, and an output signal intended to supply a signal having a level which is representative of the difference between the reference level and the video level assumed by the input signal in the course of one and the same pseudo-period, said interface circuit comprising:a first and a second sampling branch each constituted by series-arranged track-and-hold circuits, each having an input and an output, each branch having an input and an output constituted by the input of its first track-and-hold circuit and the output of its last track-and-hold circuit, respectively, the first branch comprising one track-and-hold circuit more than the second branch, the input of each branch being intended to receive the input signal from the interface circuit,a subtracter having a first input connected to the output of the first branch, a second input connected to the output of the second branch and an output constituting the output of the interface circuit,a DC level regulation loop comprising a first capacitance arranged between the input of one of the branches and the input of the interface circuit, and a first comparator having a first input connected to the output of one of the sampling branches, a second input intended to receive a regulation signal having a predetermined value and an output intended to control the conduction of a current through the first capacitance,wherein the inputs of the first and second branches are interconnected, forming a junction point connected via the first capacitance to the input of the interface circuit, andcontrol means arranged between the sampling branches and the subtracter, which means are activated when the levels of the signals at the outputs of the first and second branches correspond to the reference levels, the control means allowing for adjustment of the values of the signals at the inputs of the subtracter in order that the values are equal, andwherein the control means includesa second comparator having a first and a second input connected to the outputs of the first and second sampling branches, respectively, and an output connected via a second capacitance to a fixed voltage terminal, andan offset module having a signal input connected to the output of one of the sampling branches, a signal output connected to one of the inputs of the subtracter, the other input of which is connected to the output of the other sampling branch, the offset module also having a control input connected to the output of the second comparator and being intended to generate, between its signal input and its signal output, a potential difference whose value depends on the value of the signal received at the control input.