Imput impedance of common emitter amplifier at RF frequencie

[amal banerjee]

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.

 

[John S]

On 7/31/2019 5:25 AM, amal banerjee wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.

38.5 - j38.5 at 450MHz for a MPSH10. It changes with frequency and current.

 

On Wednesday, 31 July 2019 11:25:57 UTC+1, amal banerjee wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.

The input is a diode junction (with capacitance). So Rin depends where you are on the diode's curve. Then there's the bias cct in parallel, as well as Tr's c_in and the stray capacitances.


NT

 

[John Larkin]

On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
<dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.

The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Wed, 31 Jul 2019 11:21:47 -0400, bitrex <user@example.net> wrote:

On 7/31/19 10:22 AM, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.





Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf

It has a big table of s-params.

this is all ya get for a uhf power transistor that costs 3 bucks:

https://www.mouser.com/datasheet/2/302/BLT81_2-76125.pdf

That has a graph of Zin vs frequency, which is what the OP wanted. And
it has DC curves, unusual for an RF part.

But data sheets are generally erratic and often inaccurate. I wish we
could always get good Spice models.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[bitrex]

On 7/31/19 11:21 AM, bitrex wrote:

On 7/31/19 10:22 AM, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier
operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load
resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.





Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf

Like the part has a min CE breakdown voltage spec of 8 volts and EB
breakdown voltage spec of 5.5 volts but they give the S parameters at
VCE of 5 volts but all the graphs are done at VCE of 3 volts?

???

????????????????????

 

[bitrex]

On 7/31/19 10:22 AM, John Larkin wrote:

On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

<https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf>

this is all ya get for a uhf power transistor that costs 3 bucks:

<https://www.mouser.com/datasheet/2/302/BLT81_2-76125.pdf>

 

[John Larkin]

On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr@gmail.com wrote:

On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:

On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

 

[bitrex]

On 7/31/19 12:02 PM, John Larkin wrote:

On Wed, 31 Jul 2019 11:45:22 -0400, bitrex <user@example.net> wrote:

On 7/31/19 11:01 AM, John Larkin wrote:
On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr@gmail.com wrote:

On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.



RF small signal transistors are often intended to be used in a circuit
where the emitter is grounded, and there's a temperature stable bias
network set up to keep them biased properly with the emitter grounded,
and the datasheet specs and S parameters are measured when it's set up
like that.

On the eval boards, the "temperature stable bias network" is usually a
trimpot.

Right, they probably figure most engineering offices are climate
controlled, primarily for the engineers they tend to like to be
temperature stable, too

 

[John Larkin]

On Wed, 31 Jul 2019 11:45:22 -0400, bitrex <user@example.net> wrote:

On 7/31/19 11:01 AM, John Larkin wrote:
On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr@gmail.com wrote:

On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.



RF small signal transistors are often intended to be used in a circuit
where the emitter is grounded, and there's a temperature stable bias
network set up to keep them biased properly with the emitter grounded,
and the datasheet specs and S parameters are measured when it's set up
like that.

On the eval boards, the "temperature stable bias network" is usually a
trimpot.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[bitrex]

On 7/31/19 11:40 AM, John Larkin wrote:

On Wed, 31 Jul 2019 11:21:47 -0400, bitrex <user@example.net> wrote:

On 7/31/19 10:22 AM, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.





Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf

It has a big table of s-params.

unfortunately the S parameter table and the charts are at two different
VCEs, idk why you would use this particular transistor in a 5 volt
system it seems clearly designed for low voltage/low power applications

also you don't get anything on noise figure vs collector current

here is a good data sheet:

<http://www.hep.upenn.edu/SNO/daq/parts/mmbr941lt1.pdf>

this is all ya get for a uhf power transistor that costs 3 bucks:

https://www.mouser.com/datasheet/2/302/BLT81_2-76125.pdf

That has a graph of Zin vs frequency, which is what the OP wanted. And
it has DC curves, unusual for an RF part.

But data sheets are generally erratic and often inaccurate. I wish we
could always get good Spice models.

 

[bitrex]

On 7/31/19 11:01 AM, John Larkin wrote:

On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr@gmail.com wrote:

On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.

RF small signal transistors are often intended to be used in a circuit
where the emitter is grounded, and there's a temperature stable bias
network set up to keep them biased properly with the emitter grounded,
and the datasheet specs and S parameters are measured when it's set up
like that.

I don't know that they know how to easily make a more general model for
them that's valid under all conditions, when they're used some other
kind of way.

 

[bitrex]

On 7/31/19 12:59 PM, tabbypurr@gmail.com wrote:

On Wednesday, 31 July 2019 16:01:42 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr wrote:
On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.

I find them inaccurate at low frequencies. When I use Spice it's as often as not to model taking into account all those edge situations eg varying Vbe, beta, supply line variation & so on, and Spice is no star at that level of detail. But it helps me clarify what's going on and I can work out the realities then.

But as a general suggestion, the OP will learn a ton by getting Spice running.


NT

if u think the BJT models are bad try the JFET models sometime...

 

On Wednesday, 31 July 2019 16:01:42 UTC+1, John Larkin wrote:

On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr wrote:
On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.

I find them inaccurate at low frequencies. When I use Spice it's as often as not to model taking into account all those edge situations eg varying Vbe, beta, supply line variation & so on, and Spice is no star at that level of detail. But it helps me clarify what's going on and I can work out the realities then.

But as a general suggestion, the OP will learn a ton by getting Spice running.


NT

 

[John Larkin]

On Wed, 31 Jul 2019 11:54:42 -0400, bitrex <user@example.net> wrote:

On 7/31/19 11:40 AM, John Larkin wrote:
On Wed, 31 Jul 2019 11:21:47 -0400, bitrex <user@example.net> wrote:

On 7/31/19 10:22 AM, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.





Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf

It has a big table of s-params.

unfortunately the S parameter table and the charts are at two different
VCEs, idk why you would use this particular transistor in a 5 volt
system it seems clearly designed for low voltage/low power applications

also you don't get anything on noise figure vs collector current

here is a good data sheet:

http://www.hep.upenn.edu/SNO/daq/parts/mmbr941lt1.pdf

Is that part still available?

Most fast bipolars are gone now.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[John Larkin]

On Wed, 31 Jul 2019 13:13:12 -0400, bitrex <user@example.net> wrote:

On 7/31/19 12:59 PM, tabbypurr@gmail.com wrote:
On Wednesday, 31 July 2019 16:01:42 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr wrote:
On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.

I find them inaccurate at low frequencies. When I use Spice it's as often as not to model taking into account all those edge situations eg varying Vbe, beta, supply line variation & so on, and Spice is no star at that level of detail. But it helps me clarify what's going on and I can work out the realities then.

But as a general suggestion, the OP will learn a ton by getting Spice running.


NT


if u think the BJT models are bad try the JFET models sometime...

Some jfets have a 10:1 range of Idss on the data sheet.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[bitrex]

On 7/31/19 1:53 PM, John Larkin wrote:

On Wed, 31 Jul 2019 11:54:42 -0400, bitrex <user@example.net> wrote:

On 7/31/19 11:40 AM, John Larkin wrote:
On Wed, 31 Jul 2019 11:21:47 -0400, bitrex <user@example.net> wrote:

On 7/31/19 10:22 AM, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.





Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf

It has a big table of s-params.

unfortunately the S parameter table and the charts are at two different
VCEs, idk why you would use this particular transistor in a 5 volt
system it seems clearly designed for low voltage/low power applications

also you don't get anything on noise figure vs collector current

here is a good data sheet:

http://www.hep.upenn.edu/SNO/daq/parts/mmbr941lt1.pdf

Is that part still available?

Most fast bipolars are gone now.

IDK if it's still in production but there sure seem to be a lot of them
still out there for sale:

<https://www.digipart.com/part/mmbr941>

 

[bitrex]

On 7/31/19 1:47 PM, John Larkin wrote:

On Wed, 31 Jul 2019 13:13:12 -0400, bitrex <user@example.net> wrote:

On 7/31/19 12:59 PM, tabbypurr@gmail.com wrote:
On Wednesday, 31 July 2019 16:01:42 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 07:52:05 -0700 (PDT), tabbypurr wrote:
On Wednesday, 31 July 2019 15:23:01 UTC+1, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.

Running Spice might be easier for the OP


NT

The problem there is that the RF people rarely provide Spice models,
and I suspect that the Spice models for most transistors are
inaccurate at high frequencies. For example, they typically don't
include wire bond inductance.

I find them inaccurate at low frequencies. When I use Spice it's as often as not to model taking into account all those edge situations eg varying Vbe, beta, supply line variation & so on, and Spice is no star at that level of detail. But it helps me clarify what's going on and I can work out the realities then.

But as a general suggestion, the OP will learn a ton by getting Spice running.


NT


if u think the BJT models are bad try the JFET models sometime...

Some jfets have a 10:1 range of Idss on the data sheet.

If the choice is between using a discrete JFET in a design and eating
soap It's usually a toss-up except, if the JFET is used as a diode.

I have an old Roland drum machine that uses a JFET in the accent
circuit, some 2SK...etc part from Japan that's no longer available at
reasonable price, it went bad and it's never worked right with any of
the supposedly compatible NTE-brand subs I've tried.

 

[bitrex]

On 7/31/19 1:53 PM, John Larkin wrote:

On Wed, 31 Jul 2019 11:54:42 -0400, bitrex <user@example.net> wrote:

On 7/31/19 11:40 AM, John Larkin wrote:
On Wed, 31 Jul 2019 11:21:47 -0400, bitrex <user@example.net> wrote:

On 7/31/19 10:22 AM, John Larkin wrote:
On Wed, 31 Jul 2019 03:25:52 -0700 (PDT), amal banerjee
dakupoto@gmail.com> wrote:

Could some electronics guru here please clarify this a bit ?
What is the input impedance for a common emitter BJT amplifier operating at RF frequencies ? The output impedance id the
parallel combination of the collector resistor Rc and the load resistor. All hints, suggestionas are welcome. Thanks in advance.


The data sheets of RF transistors usually have tables of s-parameters
or Smith charts.





Some probably do, but I've noticed a lot of discrete transistor data
sheets suck just as hard as any other kind of data sheet. I've never
seen a Smith chart on one...

e.g. like this is all ya get for a transistor array that costs ten bucks?

https://www.mouser.com/datasheet/2/698/hfa3046-3096-3127-3128-1528732.pdf

It has a big table of s-params.

unfortunately the S parameter table and the charts are at two different
VCEs, idk why you would use this particular transistor in a 5 volt
system it seems clearly designed for low voltage/low power applications

also you don't get anything on noise figure vs collector current

here is a good data sheet:

http://www.hep.upenn.edu/SNO/daq/parts/mmbr941lt1.pdf

Is that part still available?

Most fast bipolars are gone now.

Here's a current manufacture one with all the nice data, and looks like
a Gummel-Poon spice model is available, too:

<https://www.nxp.com/docs/en/data-sheet/BFU520.pdf>