MMIC tolerances

[Joerg]

Still thinking about using the old BGA2001:
http://www.nxp.com/acrobat_download/datasheets/BGA2001_6.pdf

I know that the stability circles predict hail and thunder from the
north-east but I'll try my best not to let anything become inductive. It
just fits the bills nicely. Anyhow, none of the myriad MMICs that I
looked at had many entries in the min/max columns. The only entry is
usually for supply current and that varies a whole lot, like by a factor
of two between min and max. What are the typical tolerances for the
other parameters such as gain and compression point?

Side question: Is the SOT343 package likely going to remain popular? So
far I have seen it used by NXP, Avago, and Infineon.

 

[John Larkin]

Still thinking about using the old BGA2001:
http://www.nxp.com/acrobat_download/datasheets/BGA2001_6.pdf

I know that the stability circles predict hail and thunder from the
north-east but I'll try my best not to let anything become inductive. It
just fits the bills nicely. Anyhow, none of the myriad MMICs that I
looked at had many entries in the min/max columns. The only entry is
usually for supply current and that varies a whole lot, like by a factor
of two between min and max. What are the typical tolerances for the
other parameters such as gain and compression point?

For the classic InGaAs darlington mmic, you force bias current into
the output pin, so it doesn't have any choice in the matter. I've
found the gains (Mini-Circuits, Sirenza, W-J) to be very consistant,
nothing like 2:1 span.

You *can* also poke current into the input pin to shift the bias
point. Sometimes that's handy.

Any self-respecting mmic is unconditionally stable.

John

 

[maxfoo]

For the classic InGaAs darlington mmic, you force bias current into
the output pin, so it doesn't have any choice in the matter. I've
found the gains (Mini-Circuits, Sirenza, W-J) to be very consistant,
nothing like 2:1 span.

You *can* also poke current into the input pin to shift the bias
point. Sometimes that's handy.

Any self-respecting mmic is unconditionally stable.

John

Interesting, do you have an test data showing how much improvement biasing the
input pin makes? It seems like this method would only be valid if the input was
not matched to 50 ohms with the previous stage, no?

 

[Joerg]

For the classic InGaAs darlington mmic, you force bias current into
the output pin, so it doesn't have any choice in the matter. I've
found the gains (Mini-Circuits, Sirenza, W-J) to be very consistant,
nothing like 2:1 span.

Do you remember how much difference you saw in gain?

In my case more than 0.5dB would throw this application off the rocker.
Then I'd have to use an opamp and in my case I'd have to use it in
non-TIA configuration. THS4021 or something like that in standard
non-inverting fashion with the photodiode into a resistor at the
non-inverting input. Reason is that I was just informed that the PD
version can change and I don't want things to become unstable because
the new one has a different capacitance.

You *can* also poke current into the input pin to shift the bias
point. Sometimes that's handy.

Any self-respecting mmic is unconditionally stable.

Yes, I agree. But the very low NF varieties seem to all have that danger
zone up in the inductive part of the Smith chart. Actually, so do many
"roll your own" low noise amps.

 

[John Larkin]

Interesting, do you have an test data showing how much improvement biasing the
input pin makes? It seems like this method would only be valid if the input was
not matched to 50 ohms with the previous stage, no?

As long as the part is still in its linear range, pushing the bias
won't change the impedances much. For example, if the expected signal
swing range is small, you could pull up the input a bit, pulling down
the output, and run the part at lower voltage and power. I use these
parts in time-domain apps, and if I know that the signal is
predominantly in one direction (say, pulses from a microchannel plate
or a photodiode) I can bias the output in the opposite direction and
get both lower power dissipation and more peak signal swing.

Most of the ERA-type mmics are simple inside: just a darlington with a
feedback resistor, easy to model at DC.

John

 

[John Larkin]

Do you remember how much difference you saw in gain?

In my case more than 0.5dB would throw this application off the rocker.
Then I'd have to use an opamp and in my case I'd have to use it in
non-TIA configuration. THS4021 or something like that in standard
non-inverting fashion with the photodiode into a resistor at the
non-inverting input. Reason is that I was just informed that the PD
version can change and I don't want things to become unstable because
the new one has a different capacitance.



Yes, I agree. But the very low NF varieties seem to all have that danger
zone up in the inductive part of the Smith chart. Actually, so do many
"roll your own" low noise amps.

If you need extreme gain accuracy, I wouldn't use any mmic. They
wouldn't be temperature stable to a fraction of a dB... they're just
darlingtons with crappy feedback resistors. So an opamp, either as a
tia or just using a load resistor followed by a positive-gain stage
would be a lot more stable.

Have you looked at the THS4302 series? Vicious little beasts. I was
thinking of dumping a photodiode into a grounded resistor-inductor
series pair, and amping that with a THS4303 maybe. Tweak the L to
cancel some of the pd capacitance and extend the bandwidth a bit. I'd
consider a t-coil, if I understood them better, which I don't.




+30--------|<---------+------------to amp
|
|
L
|
R
|
|
gnd



John

 

[Joerg]

If you need extreme gain accuracy, I wouldn't use any mmic. They
wouldn't be temperature stable to a fraction of a dB... they're just
darlingtons with crappy feedback resistors. So an opamp, either as a
tia or just using a load resistor followed by a positive-gain stage
would be a lot more stable.

After looking at some other MMICs I have just deleted that part of the
schematic. Even the good stuff from Mini Circuits is slightly above
tolerance spec for this app. At least it's not like in the olden days
when I'd have lots of eraser turds on the floor now

So it's the load resistor opamp combo. Somehow that doesn't look
high-tech and cutting edge in terms of cost but, oh well, it'll work.

Have you looked at the THS4302 series? Vicious little beasts. ...

I don't need to go that high, just to 100MHz. Also, I'd like to get away
without more regulators and the THS4021 can live nicely with +/-12V rails.

... I was
thinking of dumping a photodiode into a grounded resistor-inductor
series pair, and amping that with a THS4303 maybe. Tweak the L to
cancel some of the pd capacitance and extend the bandwidth a bit. I'd
consider a t-coil, if I understood them better, which I don't.




+30--------|<---------+------------to amp
|
|
L
|
R
|
|
gnd

A peaker coil? That would be cool but this amp is a true hotrod. 12GHz
GBW, wow. Possibly the only way to create a reliable inductance here
would be to use one embedded in the layout. Just make sure its magnetic
field doesn't see any part of the opamp feedback.

Probably this is the frequency range where you might benefit from a
discrete design with one of those 45GHz RF transistors. Problem is that
many of these are from EU manufacturers and I have experienced
procurement nightmares there. Great products but very poor marketing.

T-coil? I've only heard that in connection with hearing aid coupler
circuits in churches and public auditoriums.

 

[John Larkin]

After looking at some other MMICs I have just deleted that part of the
schematic. Even the good stuff from Mini Circuits is slightly above
tolerance spec for this app. At least it's not like in the olden days
when I'd have lots of eraser turds on the floor now

So it's the load resistor opamp combo. Somehow that doesn't look
high-tech and cutting edge in terms of cost but, oh well, it'll work.




I don't need to go that high, just to 100MHz. Also, I'd like to get away
without more regulators and the THS4021 can live nicely with +/-12V rails.




A peaker coil? That would be cool but this amp is a true hotrod. 12GHz
GBW, wow. Possibly the only way to create a reliable inductance here
would be to use one embedded in the layout. Just make sure its magnetic
field doesn't see any part of the opamp feedback.

Probably this is the frequency range where you might benefit from a
discrete design with one of those 45GHz RF transistors. Problem is that
many of these are from EU manufacturers and I have experienced
procurement nightmares there. Great products but very poor marketing.

T-coil? I've only heard that in connection with hearing aid coupler
circuits in churches and public auditoriums.

I wish people would look up existing terminology before they make up
names. A real, classical t-coil has nothing to do with deaf people.

http://ocw.mit.edu/NR/rdonlyres/Ele...367133-8179-427C-9213-6E04B36B8A79/0/lec9.pdf


If you couple the plate of a tube to the grid of the next one, the
plate load resistor and Cp+Cg have a time constant tau, and the
bandwidth is 1/2.2tau. Adding an inductor in series with the plate
load resistor is "shunt peaking" and improves things roughly 40%.
Adding another between plate and grid is "series peaking" and helps
more. An ideal t-coil improves bandwidth 2.8 times the basic circuit.

John

 

[Joerg]

I wish people would look up existing terminology before they make up
names. A real, classical t-coil has nothing to do with deaf people.

Yeah, nowadays marketeers create such terminology. Some of the major
hearing aid companies use the word T-coil. But the term "deaf people"
isn't correct either since it's only useful for folks with some
remaining hearing ;-)

I have never really understood why magnetic loops are needed in the
first place. All the industry would have had to agree upon is a common
method of close range LF transmission.

http://ocw.mit.edu/NR/rdonlyres/Ele...367133-8179-427C-9213-6E04B36B8A79/0/lec9.pdf


If you couple the plate of a tube to the grid of the next one, the
plate load resistor and Cp+Cg have a time constant tau, and the
bandwidth is 1/2.2tau. Adding an inductor in series with the plate
load resistor is "shunt peaking" and improves things roughly 40%.
Adding another between plate and grid is "series peaking" and helps
more. An ideal t-coil improves bandwidth 2.8 times the basic circuit.

Interesting. I've seen coils in line with the plate but when they were
used to muffle a load capacitance they were often called peaker coil.
But most of the time it was there to mute unwanted oscillation way above
the operating frequency (coil wound around a resistor).

 

[Robert]

Yeah, nowadays marketeers create such terminology. Some of the major
hearing aid companies use the word T-coil. But the term "deaf people"
isn't correct either since it's only useful for folks with some remaining
hearing ;-)

I have never really understood why magnetic loops are needed in the first
place. All the industry would have had to agree upon is a common method of
close range LF transmission.



Interesting. I've seen coils in line with the plate but when they were
used to muffle a load capacitance they were often called peaker coil. But
most of the time it was there to mute unwanted oscillation way above the
operating frequency (coil wound around a resistor).

Thomas Lee's got a nice write-up of the different ways to do Inductive
Peaking including the Bridged T-Coil in:
The Design of CMOS Radio-Frequency Integrated Circuits, Second Edition
(Hardcover)
http://www.amazon.com/Design-Radio-Frequency-Integrated-Circuits-Second/dp/0521835399

I also liked his first chapters on the early history of Radio Circuits as
well but a lot of people don't like what they call his "disdain of rigor".

Robert

 

[Joerg]

John Larkin wrote:

[snip]

... I was
thinking of dumping a photodiode into a grounded resistor-inductor
series pair, and amping that with a THS4303 maybe. Tweak the L to
cancel some of the pd capacitance and extend the bandwidth a bit. I'd
consider a t-coil, if I understood them better, which I don't.



+30--------|<---------+------------to amp
|
|
L
|
R
|
|
gnd



A peaker coil? That would be cool but this amp is a true hotrod. 12GHz
GBW, wow. Possibly the only way to create a reliable inductance here
would be to use one embedded in the layout. Just make sure its magnetic
field doesn't see any part of the opamp feedback.

Probably this is the frequency range where you might benefit from a
discrete design with one of those 45GHz RF transistors. Problem is that
many of these are from EU manufacturers and I have experienced
procurement nightmares there. Great products but very poor marketing.

T-coil? I've only heard that in connection with hearing aid coupler
circuits in churches and public auditoriums.


I wish people would look up existing terminology before they make up
names. A real, classical t-coil has nothing to do with deaf people.

Yeah, nowadays marketeers create such terminology. Some of the major
hearing aid companies use the word T-coil. But the term "deaf people"
isn't correct either since it's only useful for folks with some remaining
hearing ;-)

I have never really understood why magnetic loops are needed in the first
place. All the industry would have had to agree upon is a common method of
close range LF transmission.

http://ocw.mit.edu/NR/rdonlyres/Ele...367133-8179-427C-9213-6E04B36B8A79/0/lec9.pdf


If you couple the plate of a tube to the grid of the next one, the
plate load resistor and Cp+Cg have a time constant tau, and the
bandwidth is 1/2.2tau. Adding an inductor in series with the plate
load resistor is "shunt peaking" and improves things roughly 40%.
Adding another between plate and grid is "series peaking" and helps
more. An ideal t-coil improves bandwidth 2.8 times the basic circuit.

Interesting. I've seen coils in line with the plate but when they were
used to muffle a load capacitance they were often called peaker coil. But
most of the time it was there to mute unwanted oscillation way above the
operating frequency (coil wound around a resistor).

Thomas Lee's got a nice write-up of the different ways to do Inductive
Peaking including the Bridged T-Coil in:
The Design of CMOS Radio-Frequency Integrated Circuits, Second Edition
(Hardcover)
http://www.amazon.com/Design-Radio-Frequency-Integrated-Circuits-Second/dp/0521835399

Amazon now want my email address before allowing to preview. What are
they thinking? Or, are they thinking?

I also liked his first chapters on the early history of Radio Circuits as
well but a lot of people don't like what they call his "disdain of rigor".

Yeah, not scientific enough probably. I like those books. Have to look
next time at Borders. Although I am not sure I'll go there anymore
because ours has shrunk the EE section to almost zero :-(

 

[John Larkin]

Thomas Lee's got a nice write-up of the different ways to do Inductive
Peaking including the Bridged T-Coil in:
The Design of CMOS Radio-Frequency Integrated Circuits, Second Edition
(Hardcover)
http://www.amazon.com/Design-Radio-Frequency-Integrated-Circuits-Second/dp/0521835399

I also liked his first chapters on the early history of Radio Circuits as
well but a lot of people don't like what they call his "disdain of rigor".

Robert

Other good books that disdain rigor:

AoE

Phil Hobbs' "Building Electro-Optical Systems". Full of quirky
quotations, cartoons, lore. Also dense with good stuff.

Thomas Lee's "Planar Microwave Engineering." But I don't know why he
calls it "Planar", since it covers most everything.

All three are worth reading cover to cover.

John