US 6,720,828 B2Granted

Apparatus and method for compensating a high impedance attenuator

AssigneeTektronix, Inc.

InventorsTheodore G. Nelson, Michael P. Khaw, Daniel G. Knierim, John F. Stoops

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Abstract

A high impedance attenuator for use in a test and measurement instrument employs compensation to adjust the low frequency attenuation to match the high frequency attenuation exhibited by the attenuator, rather than attempting to adjust the high frequency attenuation exhibited by the attenuator. In an alternate embodiment of the invention, compensation to adjust low frequency attenuation is employed in a feedback loop and an opposite compensation is applied in a parallel attenuation stage to stabilize the input resistance. In yet another embodiment of the invention, compensation to adjust low frequency attenuation is employed by means of an R-C time constant of an additional R-C circuit in a feed forward loop. This additional time constant is matched to the R-C time constant of the input R-C network. The input resistance of the attenuator is not changed.

Claims5

Dependent claims

An electronically adjustable attenuator, comprising:

an input terminal and an output terminal;
a resistive-capacitive voltage divider having at least a first capacitor coupled between said input and output terminals for conveying high frequency signals from said input terminal to said output terminal and at least a first resistor coupled in parallel with said at least first capacitor for conveying low frequency signals between said input terminal and said output terminal with said at least first capacitor and said at least first resistor having a common center tap coupled to at least a second capacitor coupled between said common center tap of said capacitor and resistor and a point of reference potential and at least a second resistor coupled to said common center tap;
a variable gain amplifier having an input terminal coupled to said common center tap of said at least first capacitor and resistor and having output terminal coupled to the other end of said at least second resistor for providing gain adjusted low frequency signals;
an inverting amplifier for receiving said gain adjusted low frequency signals, and generating an inverted representation of said gain adjusted low frequency signals at an output;
and
a resistive path coupled between said output of said inverting amplifier and said input terminal of said attenuator for conveying said inverted representation of said gain adjusted low frequency signals to said input terminal of said attenuator, wherein said attenuator is compensated by adjusting gain of said low frequency signals conveyed by said low frequency signal path.

3 more elements

Dependencies are inferred from the claim text.