[hpsdr] High Power Amplifiers - Tracking Power Supplies

[Phil Harman]

Hi Jim,

Thanks for the contribution - the TDA8954 looks like a most useful device.

We should be able to make a very simple, but effective, tracking power
supply by driving the gates (via suitable driver chips) of a a pair of
complementary FETs directly from the Penelope FPGA.

Bill, KD5TFD, has a command line option in his HPSDR version of
PowerSDR(TM) to send envelope and phase rather than I&Q to Penny.  We can
use the envelope signal to drive the FETs and the phase to modulate the RF
drive (i.e. phase modulate the CORDIC).

I did some simple tests a while ago using a cheap switching FET as a 160m
Class E PA and it worked impressively well. See
<http://openhpsdr.org/wiki/index.php?title=THOR> and also the work by
Steve, G1YLB, who is working on this project.

One of the issues in the past with such designs has been to problem of
maintaining the phase relationship between the envelope and phase signals.

Given the high clock speed we use on Penny it should be straightforward to
tweak these to always give an optimum result.

Fertile ground for experimentation!

73's Phil...VK6APH





> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi,
>
> Thanks to all for the excellent contributions to this list.
>
> Just to comment on what many may already know, tracking power supplies
> have been used sucessfully
> for quite some time. A decade or more ago, Bob Carver used one in an
> audio power amplifier, Sunfire I
> think. As I recall, it maintained the DC supplies about 6V greater than
> the required value the amp needed
> for the signal at any given moment. They sounded great to me and had low
> dissipation for a multi-FET design.
>
> And if memory serves, the principle dates back even further.
>
> There are some excellent high power class-d integrated amplifier chips
> now, like the TDA8954, which might
> potentially serve as the starting point for a tracking supply. Capable
> of 400+w, about $9USD.
>
> Best,
>
> Jim Rothwell
> St. Ann, MO
>  ----------
> Date: Fri, 23 Jul 2010 12:24:07 +0200
>
>>From: "Ben Witvliet" <pa5bw at xs4all.nl>
>>To: <hpsdr at lists.openhpsdr.org>
>>Subject: [hpsdr] EER finals, predistortion
>>Message-ID: <002101cb2a51$2ef7cb20$8ce76160$@nl>
>>Content-Type: text/plain; charset="iso-8859-1"
>>
>>Dear all,
>>
>>
>>
>>I found the following (commercial) publication on very high efficiency RF
>>power amplifiers:
>>
>>
>><http://www.mathworks.nl/company/newsletters/digest/2010/july/nujira-amplifi
>>er-performance.html?s_v1=13445411_1-6XCKGU>
>>http://www.mathworks.nl/company/newsletters/digest/2010/july/nujira-amplifie
>>r-performance.html?s_v1=13445411_1-6XCKGU
>>
>>It is of course a success story describing the benefit of their own
>> product,
>>but the message I get from it: EER as we meant to achieve in Thor can be
>>done.
>>
>>
>>
>>Also the article mentions the use of predistortion to create a very
>> linear
>>amplifier. I heard that before from an English consultant (For my QRL I
>>participate in European standardization work). He said that mobile phone
>>network operators had great success with predistortion to get rid of IMD
>>products on combined installations. So I see the remark in this document
>> as
>>a confirmation that that has become feasible with ?average? means. I
>> haven?t
>>seen any amateur publications yet on the use of non-linear or
>> not-so-linear
>>amplifiers and predistortion. With the processing power we have in HPSDR
>>this may come within reach.
>>
>>
>>
>>By the way: as a MatLab user I?m very interested in using Simulink to
>>simulate such applications. Makes it possible to replace the MatLab
>> software
>>blocks bit-by-bit by real-life hardware.
>>
>>
>>
>>Justed wanted to share this information with you.
>>
>>
>>
>>
>>
>>
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