Patent ID: 7634370
Filing Date: 2009-12-15
Classification: G01R

Abstract:
1. A waveform input circuit, comprising: an input signal transmission line having a predetermined characteristic impedance to receive a signal from a device under test at one end and outputs the signal at another end; an input buffer connected to said another end of the input signal transmission line to receive the signal from the device under test as an input signal; a high input impedance terminating resistance connected to an input terminal of the input buffer; a low input terminating resistance connected to the input terminal of the input buffer where the low input terminating resistance is impedance-matched with the characteristic impedance of the input signal transmission line; selection means for selecting one of the high input and low input terminating resistances; switch means for supplying one of at least two different reference potentials to the input signal transmission line; and an envelope drive amplifier connected between the input buffer and the switch means to provide one reference potential which is responsive to an output potential of the input buffer to an envelope of the input signal transmission line through the switch means; wherein said envelope is an outer conductor of the input signal transmission line, and said signal from the device under test is transmitted through an inner conductor of the input signal transmission line; and wherein said one reference potential switched by the switch means is an in phase potential which is a potential controlled to be in phase with the input signal by an output voltage of the input buffer which is connected when the high input impedance terminating resistance is selected in the selection means.