On 05/14/2017 07:14 PM, John Larkin wrote:> On Sun, 14 May 2017 21:53:32 GMT, Steve Wilson <no@spam.com> wrote: > >> John Larkin <jjlarkin@highlandtechnology.com> wrote: >> >>> The TI THS series really screams. There are parts with 1.8 GHz GBW and >>> huge output currents. Or the Analog Devices AD800x parts. >> >> Both are slow. 2GHz or so. > > But the TI parts have huge voltage swing and current capability. > Everyone else is ratcheting down voltage as speed goes up. > >> >> These look interesting: >> >> LTC6268 4GHz >> http://www.linear.com/docs/46371 > > Impressive, except for the 5 volt supply. > >> >> LTC6409 10GHz 1.1nV/rt(Hz) >> http://www.linear.com/docs/29893 >> >> > > I used a similar part, LTC6402 differential ADC driver. It was flakey, > so we had to redesign with an ADA4950. > >For 6 bucks they better be hand-crafted by the Gnomes of Zurich!
Fast buffer idea
Started by ●May 14, 2017
Reply by ●May 14, 20172017-05-14
Reply by ●May 14, 20172017-05-14
John Larkin <jjlarkin@highlandtechnology.com> wrote:>> LTC6409 10GHz 1.1nV/rt(Hz) >> http://www.linear.com/docs/29893> I used a similar part, LTC6402 differential ADC driver. It was flakey, > so we had to redesign with an ADA4950.The LTC6402 is nowhere near similar to the LTC6409. Fixed 20db gain, 300MHz BW vs unity gain stable, 10GHz GBW. Totally different devices. I'm surprised you had problems with LTC. They usually have a petty good reputation for quality.
Reply by ●May 14, 20172017-05-14
bitrex wrote...> > On 05/14/2017 03:28 PM, Kevin Aylward wrote: > >> I haven't examined the effectiveness of the additional boost circuit, >> but it is important to make sure the basic design is optimised first. >> Typically, something like a 1:4 build up in current from the first bip >> follower to the second bip follower. In an asic design I might use the >> same current and use multiple devices in parallel. I would suggest >> trying an active current source to the input followers, to get the drive >> to the second follower, and remove the boost circuit. Use standard >> configurations, until you can prove that a bright idea is truly better. > > The problem with a simple active current source to the input followers > is quiescent current draw - if you optimize the follower current source > for the gain you need at the highest frequency the buffer draws a huge > helping of quiescent current sitting around doing nothing.Devices that are off, or mostly off, are slow to turn on. You suffer from a t = C V / i delay time. SPICE fails to give you the proper value for C, and the delay for i. This is especially true if you invoke any MOSFET models. You can make SPICE devices do all kinds of amazing things. This is NOT to say the real device can do the same thing. -- Thanks, - Win
Reply by ●May 14, 20172017-05-14
On Sunday, May 14, 2017 at 12:19:51 PM UTC-7, Steve Wilson wrote:> What are your recommendations to handle a 100MHz square wave?LMH5401 and LTC6409 are both good parts. Or an AD8000 for that matter, depending on how many harmonics you want to keep. -- john, KE5FX
Reply by ●May 14, 20172017-05-14
"John Miles, KE5FX" <jmiles@gmail.com> wrote:> On Sunday, May 14, 2017 at 12:19:51 PM UTC-7, Steve Wilson wrote: >> What are your recommendations to handle a 100MHz square wave? > > LMH5401 and LTC6409 are both good parts. > > Or an AD8000 for that matter, depending on how many harmonics you want > to keep. > > -- john, KE5FXLMH5401 �s another one for the collection. Good info. Thanks
Reply by ●May 15, 20172017-05-15
On Sun, 14 May 2017 19:59:50 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 05/14/2017 07:14 PM, John Larkin wrote: >> On Sun, 14 May 2017 21:53:32 GMT, Steve Wilson <no@spam.com> wrote: >> >>> John Larkin <jjlarkin@highlandtechnology.com> wrote: >>> >>>> The TI THS series really screams. There are parts with 1.8 GHz GBW and >>>> huge output currents. Or the Analog Devices AD800x parts. >>> >>> Both are slow. 2GHz or so. >> >> But the TI parts have huge voltage swing and current capability. >> Everyone else is ratcheting down voltage as speed goes up. >> >>> >>> These look interesting: >>> >>> LTC6268 4GHz >>> http://www.linear.com/docs/46371 >> >> Impressive, except for the 5 volt supply. >> >>> >>> LTC6409 10GHz 1.1nV/rt(Hz) >>> http://www.linear.com/docs/29893 >>> >>> >> >> I used a similar part, LTC6402 differential ADC driver. It was flakey, >> so we had to redesign with an ADA4950. >> >> > >For 6 bucks they better be hand-crafted by the Gnomes of Zurich!A part like that would generally feed an $80 ADC. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●May 15, 20172017-05-15
On Mon, 15 May 2017 00:16:33 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highlandtechnology.com> wrote: > >>> LTC6409 10GHz 1.1nV/rt(Hz) >>> http://www.linear.com/docs/29893 > >> I used a similar part, LTC6402 differential ADC driver. It was flakey, >> so we had to redesign with an ADA4950. > >The LTC6402 is nowhere near similar to the LTC6409. > >Fixed 20db gain, 300MHz BW vs unity gain stable, 10GHz GBW. Totally >different devices.12 db gain. It tended to oscillate at large swings.> >I'm surprised you had problems with LTC. They usually have a petty good >reputation for quality.We were surprised too. And annoyed that we had to spin the board. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●May 15, 20172017-05-15
On 05/14/2017 08:58 PM, Winfield Hill wrote:> bitrex wrote... >> >> On 05/14/2017 03:28 PM, Kevin Aylward wrote: >> >>> I haven't examined the effectiveness of the additional boost circuit, >>> but it is important to make sure the basic design is optimised first. >>> Typically, something like a 1:4 build up in current from the first bip >>> follower to the second bip follower. In an asic design I might use the >>> same current and use multiple devices in parallel. I would suggest >>> trying an active current source to the input followers, to get the drive >>> to the second follower, and remove the boost circuit. Use standard >>> configurations, until you can prove that a bright idea is truly better. >> >> The problem with a simple active current source to the input followers >> is quiescent current draw - if you optimize the follower current source >> for the gain you need at the highest frequency the buffer draws a huge >> helping of quiescent current sitting around doing nothing. > > Devices that are off, or mostly off, are slow to turn on. > You suffer from a t = C V / i delay time. SPICE fails > to give you the proper value for C, and the delay for i. > This is especially true if you invoke any MOSFET models.The Spice models for discrete transistors are so rough that they don't even model the device capacitances and charge storage effects correctly?
Reply by ●May 15, 20172017-05-15
On Sun, 14 May 2017 16:10:04 -0400, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 05/14/2017 03:28 PM, Kevin Aylward wrote: > >> I haven't examined the effectiveness of the additional boost circuit, >> but it is important to make sure the basic design is optimised first. >> Typically, something like a 1:4 build up in current from the first bip >> follower to the second bip follower. In an asic design I might use the >> same current and use multiple devices in parallel. I would suggest >> trying an active current source to the input followers, to get the drive >> to the second follower, and remove the boost circuit. Use standard >> configurations, until you can prove that a bright idea is truly better. > >The problem with a simple active current source to the input followers >is quiescent current draw - if you optimize the follower current source >for the gain you need at the highest frequency the buffer draws a huge >helping of quiescent current sitting around doing nothing. > >IC implementations solve this in various clever ways using - you guessed >it - _more_ active current sources.Analog ICs can use basically unlimited numbers of radical parts, and have essentially no interconnect parasitics. And they can spend a lot of money on design. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●May 15, 20172017-05-15
John Larkin <jjlarkin@highlandtechnology.com> wrote:> 12 db gain. It tended to oscillate at large swings.Are you talking about a different device? There doesn't seem to be any way to change the gain of the LTC6402 except by adding external feedback. This may cause enough phase shift to produce the oscillations.>>I'm surprised you had problems with LTC. They usually have a petty good >>reputation for quality.> We were surprised too. And annoyed that we had to spin the board.Did you send your data to LTC?
