The Cyber-Spy.Com Usenet Archive Feeds Directly From The Open And Publicly Available Newsgroup Sci.Electronics.Design
This Group And Thousands Of Others Are Available On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic, Opinions Or Content Posted To This Or Any Other Newsgroup. This Web Archive Of The Newsgroup And Posts Are For Informational Purposes Only.
From: John Larkin
Newsgroups: sci.electronics.design
Subject: Re: DSP 2's complement vs straight binary
Date: Thu, 17 Oct 2002 21:09:50 -0700
Organization: Posted via Supernews, http://www.supernews.com
Message-ID: <442vqugt2apqghc7jio3fgbdal7l5hi8lf@4ax.com>
References: <2kpuqu8ljk8481qiju27jrb1vj171hbe1l@4ax.com>
X-Newsreader: Forte Agent 1.91/32.564
On Fri, 18 Oct 2002 03:07:07 GMT, "Thomas Magma"
wrote:
>If you were to simply invert the MSB it would convert the binary number to
>something called a "sign magnitude" and not to 2's complement. 2's
>complement is how higher level programming languages treats its 'byte'
>literals, this what I need.
>
>Thomas
>
>"John Larkin" wrote in
>message news:2kpuqu8ljk8481qiju27jrb1vj171hbe1l@4ax.com...
>> On Fri, 18 Oct 2002 01:08:36 GMT, "Thomas Magma"
>> wrote:
>>
>> >Hello,
>> >
>> >I am involved in a project where we sub-sample the IF, store it to memory
>> >and then post-process it. We are at the stage of selecting a ADC for the
>> >project. I have noticed that a lot of the ADC's suitable for this design
>> >only output straight binary. All of my algorithms to date have used 2's
>> >complement (signed) values to perform DFT or FFT functions. Processing
>speed
>> >is a major concern and we don't have time to convert each binary sample
>to
>> >2's complement. Is there an equivalent method of the DFT or FFT that uses
>> >straight binary? Or does anybody know of a 3V ADC that puts out 2's
>> >compliment and can sub-sample 10.7mhz at less than 1mhz (pipeline)?
>> >
>> >Thanks.
>> >
>>
>>
>> You can't just invert the MSB?
>>
>>
>> John
>>
>
No, really. Quote from an Analog Devices datasheet:
Digital Outputs
The AD9221/AD9223/AD9220 output data is presented in
positive true straight binary for all input ranges. Table IV indi-
cates the output data formats for various input ranges regardless
of the selected input range. A twos complement output data
format can be created by inverting the MSB.
So you could do this with one XOR instruction, or just stick a
hardware inverter in the MSB data line.
John
Go Back To The Cyber-Spy.Com Usenet Web Archive Index Of The sci.electronics.design Newsgroup
|