Cross post from QRP0-L: Si598 vs Si570 and the FREEZE-M capability
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Alex Lee
Oct 29, 2010, 9:50:55 PM10/29/10
to MOBOKITS
Hi Loftur et al,
Interesting post copied below. Main points: Si570 has better phase
noise than Si598. The Si570 has an "undocumented" FREEZE-M capability
(which the Si598 has documented), which is supposed to prevent
spurious DCO output during small freq changes. I don't know whether
this applies to the "smooth tune" that we are currently using.
73 Alex
Message: 19
Date: Thu, 28 Oct 2010 19:53:12 -0500
From: "Craig Johnson, AA0ZZ" <aa...@cbjohns.com>
Subject: Re: [QRP-L] Si598
To: "QRP-L" <qr...@mailman.qth.net>
Message-ID: <F6468F27BDE04088B0F390931A17CB1C@P8>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Hi Paul,
>Anyone taken a look at the new Si598 yet?
>Reported to be an improved Si570 and at a lower price.
>
>Paul, 5B8BA
Yes! I just took a 1-month "detour" to investigate this even-newer
part because it
looked like there were some significant advantages in switching from
the Si570 to the
Si598, The Si598 is several dollars cheaper, it looks like Mouser is
going to stock
them (at least some varieties) and it looked like the Si598 had a new
capability - the
FREEZE-M - which was not in the Si570. The FREEZE-M (not to be
confused with the
FREEZE-DCO which must always be used for large frequency excursions
and causes the 10ms
RF dropouts) is used for small frequency changes with the DCO
continuing to run. The
FREEZE-M prevents the "spraying" of RF of unknown frequencies while
the six control
bytes are being loaded into the device. This capability was new in
the Si598 spec and
was not in the Si570 spec. I thought these reasons were sufficient so
I was ready to
jump. I updated the tables in my code (to accommodate the new
internal clock
frequency), bought some parts from Mouser and gave it a spin. Yes, it
works fine.
The fact that I am using the CMOS variety, the max frequency of 160
MHz was the same
as for the Si570 so it was not an issue.
However, as of a few days ago I have just switched back to the Si570.
The reason -
performance. At one time my "friendly local salesman" told me that he
had heard that
the Si570 was the "Cadillac" and the Si598 is the "Chevy" but couldn't
give me details
as to why. In making the change, I had a minor issue getting the
FREEZE-M capability
in the Si598 to work properly so I had a good Email discussion with a
Silicon Labs tech
support guy. After he answered my questions and I was able to get it
working, I asked
him about the advantages of the Si570 over the Si598. He told me that
the Si570 has
lower phase noise than the Si598 primarily due to crystal selection.
The Si570 uses a
3rd overtone 114.285 MHz crystal as a reference versus the more
economical 39.17 MHz
fundamental mode crystal used by the Si598. Therefore the update rate
of the Si570's
PLL is higher than the Si598's PLL. Generally speaking, the higher
the update rate,
the higher the S/N ratio, and the lower the overall phase noise. This
is most
noticeable in the mid-range offset frequencies where phase detector
noise contributes.
By the way, he also told me that the Si570 ALSO has the FREEZE-M
capability; it is shown
in the latest version of the spec sheet and just wasn't in the older
version of the spec
sheet that I was using. That meant that the only real difference that
remained was the
price.
Granted, the Si598 performance may be perfectly sufficient for some
applications but I
am not willing to sacrifice better phase noise for a couple of
dollars.
Best Regards,
-Craig, AA0ZZ
Interesting post copied below. Main points: Si570 has better phase
noise than Si598. The Si570 has an "undocumented" FREEZE-M capability
(which the Si598 has documented), which is supposed to prevent
spurious DCO output during small freq changes. I don't know whether
this applies to the "smooth tune" that we are currently using.
73 Alex
Message: 19
Date: Thu, 28 Oct 2010 19:53:12 -0500
From: "Craig Johnson, AA0ZZ" <aa...@cbjohns.com>
Subject: Re: [QRP-L] Si598
To: "QRP-L" <qr...@mailman.qth.net>
Message-ID: <F6468F27BDE04088B0F390931A17CB1C@P8>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original
Hi Paul,
>Anyone taken a look at the new Si598 yet?
>Reported to be an improved Si570 and at a lower price.
>
>Paul, 5B8BA
Yes! I just took a 1-month "detour" to investigate this even-newer
part because it
looked like there were some significant advantages in switching from
the Si570 to the
Si598, The Si598 is several dollars cheaper, it looks like Mouser is
going to stock
them (at least some varieties) and it looked like the Si598 had a new
capability - the
FREEZE-M - which was not in the Si570. The FREEZE-M (not to be
confused with the
FREEZE-DCO which must always be used for large frequency excursions
and causes the 10ms
RF dropouts) is used for small frequency changes with the DCO
continuing to run. The
FREEZE-M prevents the "spraying" of RF of unknown frequencies while
the six control
bytes are being loaded into the device. This capability was new in
the Si598 spec and
was not in the Si570 spec. I thought these reasons were sufficient so
I was ready to
jump. I updated the tables in my code (to accommodate the new
internal clock
frequency), bought some parts from Mouser and gave it a spin. Yes, it
works fine.
The fact that I am using the CMOS variety, the max frequency of 160
MHz was the same
as for the Si570 so it was not an issue.
However, as of a few days ago I have just switched back to the Si570.
The reason -
performance. At one time my "friendly local salesman" told me that he
had heard that
the Si570 was the "Cadillac" and the Si598 is the "Chevy" but couldn't
give me details
as to why. In making the change, I had a minor issue getting the
FREEZE-M capability
in the Si598 to work properly so I had a good Email discussion with a
Silicon Labs tech
support guy. After he answered my questions and I was able to get it
working, I asked
him about the advantages of the Si570 over the Si598. He told me that
the Si570 has
lower phase noise than the Si598 primarily due to crystal selection.
The Si570 uses a
3rd overtone 114.285 MHz crystal as a reference versus the more
economical 39.17 MHz
fundamental mode crystal used by the Si598. Therefore the update rate
of the Si570's
PLL is higher than the Si598's PLL. Generally speaking, the higher
the update rate,
the higher the S/N ratio, and the lower the overall phase noise. This
is most
noticeable in the mid-range offset frequencies where phase detector
noise contributes.
By the way, he also told me that the Si570 ALSO has the FREEZE-M
capability; it is shown
in the latest version of the spec sheet and just wasn't in the older
version of the spec
sheet that I was using. That meant that the only real difference that
remained was the
price.
Granted, the Si598 performance may be perfectly sufficient for some
applications but I
am not willing to sacrifice better phase noise for a couple of
dollars.
Best Regards,
-Craig, AA0ZZ
Alex Lee
Oct 29, 2010, 9:47:22 PM10/29/10
to MOBOKITS
Loftur Jónasson
Oct 30, 2010, 8:34:36 PM10/30/10
to mobo...@googlegroups.com
Hi Alex & all,
I just had a look at the datasheet for the Si598. As far as I can see the Si570 and Si598 are compatible at the register control level, and both have the same and equally well documented "smooth tune" capability for frequency jumps within +/- 3500ppm of the original frequency. It may be possible that this "smoothtune method was not documented in the very first datasheets for the Si570, but as of when I started fiddling with it, this facility was documented.
To sum it up, it appears that the Si598 is a bit cheaper version of the Si570, identical in most respects, but with a lower frequency internal crystal oscillator and a bit higher phase noise, probably still within any reasonable requirements for HF use.
:)
73 de Loftur, ve/tf3lj
2010/10/30 Alex Lee <alexl...@gmail.com>
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