Integrated digitally controlled linear-in-decibels attenuator
AssigneeNational Semiconductor Corporation
InventorHon Kin Chiu
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Abstract
An integrated digitally controlled linear-in-decibels attenuator circuit in which one or more sets of selection switches establish a desired attenuation by selectively connecting the input signal electrode to one or more corresponding resistive ladder networks connected in series, thereby providing a substantially more constant signal attenuation value over a wider frequency bandwidth. With a single resistive ladder network, attenuation control is achieved using a thermometer switching code. With multiple resistive ladder networks, coarse and fine attenuation control can be achieved using thermometer and bubble switching codes, respectively.
Claims13
-20. (canceled)
An apparatus including an integrated digitally controlled linear-in-decibels attenuator circuit, comprising:
- first switched resistance circuitry responsive to a first plurality of digital control signals by attenuating an input signal to provide a first attenuated signal having a magnitude substantially in accordance with one of a first plurality of attenuation values mutually separated by a first attenuation step substantially in accordance with a thermometer code;
- and
- second switched resistance circuitry coupled to said first switched resistance circuitry and responsive to a second plurality of digital control signals by attenuating said first attenuated signal to provide a second attenuated signal having a magnitude substantially in accordance with one of a second plurality of attenuation values mutually separated by a second attenuation step substantially in accordance with a bubble code, wherein said second attenuation step is smaller than said first attenuation step;
- wherein a ratio of said second attenuated signal and said input signal is one of a plurality of ratio values mutually separated by linear-in-decibels steps.
A method for attenuating a signal in a linear-in-decibels manner in accordance with a plurality of digital control signals, comprising:
- attenuating an input signal in accordance with a first plurality of digital control signals to provide a first attenuated signal having a magnitude substantially in accordance with one of a first plurality of attenuation values mutually separated by a first attenuation step substantially in accordance with a thermometer code;
- and
- attenuating said first attenuated signal in accordance with a second plurality of digital control signals to provide a second attenuated signal having a magnitude substantially in accordance with one of a second plurality of attenuation values mutually separated by a second attenuation step substantially in accordance with a bubble code, wherein said second attenuation step is smaller than said first attenuation step;
- wherein a ratio of said second attenuated signal and said input signal is one of a plurality of ratio values mutually separated by linear-in-decibels steps.
Dependencies are inferred from the claim text.