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From: Bitrex on 9 May 2010 01:40
miso(a)sushi.com wrote:
> On May 8, 8:01 pm, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>> John Larkin wrote:
>>> On Sat, 08 May 2010 20:19:15 -0400, Bitrex
>>> <bit...(a)de.lete.earthlink.net> wrote:
>>>> If you put a reference current into the collector of one half of a
>>>> differential pair,
>>> You've lost me already. What do you mean by putting a current into the
>>> collector of a diff pair? Normally one stuffs a current into the
>>> paralleled emitters.
>>> Can you post a schematic?
>>> John
>> Sorry for not being more clear - in the meantime I was able to find a
>> website that has an example of the circuit configuration I am talking
>> about here, figure 3:
>>
>> http://www.uni-bonn.de/~uzs159/
>>
>> It appears from the text the most common way to compensate the 1/T
>> temperature dependence of the circuit is to use a resistor with a
>> positive temperature coefficient in the circuit that provides the
>> control voltage. To make it work well I guess you would want to bind
>> the differential pair to the tempco resistor with some kind of thermally
>> conductive adhesive.
>>
>>
>>
>>> and then take an output current from the collector of
>>>> the other transistor of a differential pair, the output current as a
>>>> fraction of the reference current will be compensated against variations
>>>> of Is. However, because of the dependence of VT on temperature Vbe will
>>>> now have a positive tempco, and the output current as a fraction of
>>>> the reference current will decrease with increasing temperature of the
>>>> pair. I'm wondering what strategies the analog designers here have used
>>>> to compensate for this second-order temperature dependence? TIA!
>
> Looks like frames did you a disservice. It this the page in question?
> http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
>
> If not, then right click on the link in question and open it in
> another window to get the correct URL.

Thanks, that's the correct page.
From: Jim Thompson on 9 May 2010 11:46
On Sun, 09 May 2010 01:40:53 -0400, Bitrex
<bitrex(a)de.lete.earthlink.net> wrote:

>miso(a)sushi.com wrote:
>> On May 8, 8:01 pm, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>>> John Larkin wrote:
>>>> On Sat, 08 May 2010 20:19:15 -0400, Bitrex
>>>> <bit...(a)de.lete.earthlink.net> wrote:
>>>>> If you put a reference current into the collector of one half of a
>>>>> differential pair,
>>>> You've lost me already. What do you mean by putting a current into the
>>>> collector of a diff pair? Normally one stuffs a current into the
>>>> paralleled emitters.
>>>> Can you post a schematic?
>>>> John
>>> Sorry for not being more clear - in the meantime I was able to find a
>>> website that has an example of the circuit configuration I am talking
>>> about here, figure 3:
>>>
>>> http://www.uni-bonn.de/~uzs159/
>>>
>>> It appears from the text the most common way to compensate the 1/T
>>> temperature dependence of the circuit is to use a resistor with a
>>> positive temperature coefficient in the circuit that provides the
>>> control voltage. To make it work well I guess you would want to bind
>>> the differential pair to the tempco resistor with some kind of thermally
>>> conductive adhesive.
>>>
>>>
>>>
>>>> and then take an output current from the collector of
>>>>> the other transistor of a differential pair, the output current as a
>>>>> fraction of the reference current will be compensated against variations
>>>>> of Is. However, because of the dependence of VT on temperature Vbe will
>>>>> now have a positive tempco, and the output current as a fraction of
>>>>> the reference current will decrease with increasing temperature of the
>>>>> pair. I'm wondering what strategies the analog designers here have used
>>>>> to compensate for this second-order temperature dependence? TIA!
>>
>> Looks like frames did you a disservice. It this the page in question?
>> http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
>>
>> If not, then right click on the link in question and open it in
>> another window to get the correct URL.
>
>Thanks, that's the correct page.

What _exactly_ are you trying to do... compensate a diff pair gain
over temperature?

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The only thing bipartisan in this country is hypocrisy
From: Bitrex on 9 May 2010 18:59
Jim Thompson wrote:
> On Sun, 09 May 2010 01:40:53 -0400, Bitrex
> <bitrex(a)de.lete.earthlink.net> wrote:
>
>> miso(a)sushi.com wrote:
>>> On May 8, 8:01 pm, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>>>> John Larkin wrote:
>>>>> On Sat, 08 May 2010 20:19:15 -0400, Bitrex
>>>>> <bit...(a)de.lete.earthlink.net> wrote:
>>>>>> If you put a reference current into the collector of one half of a
>>>>>> differential pair,
>>>>> You've lost me already. What do you mean by putting a current into the
>>>>> collector of a diff pair? Normally one stuffs a current into the
>>>>> paralleled emitters.
>>>>> Can you post a schematic?
>>>>> John
>>>> Sorry for not being more clear - in the meantime I was able to find a
>>>> website that has an example of the circuit configuration I am talking
>>>> about here, figure 3:
>>>>
>>>> http://www.uni-bonn.de/~uzs159/
>>>>
>>>> It appears from the text the most common way to compensate the 1/T
>>>> temperature dependence of the circuit is to use a resistor with a
>>>> positive temperature coefficient in the circuit that provides the
>>>> control voltage. To make it work well I guess you would want to bind
>>>> the differential pair to the tempco resistor with some kind of thermally
>>>> conductive adhesive.
>>>>
>>>>
>>>>
>>>>> and then take an output current from the collector of
>>>>>> the other transistor of a differential pair, the output current as a
>>>>>> fraction of the reference current will be compensated against variations
>>>>>> of Is. However, because of the dependence of VT on temperature Vbe will
>>>>>> now have a positive tempco, and the output current as a fraction of
>>>>>> the reference current will decrease with increasing temperature of the
>>>>>> pair. I'm wondering what strategies the analog designers here have used
>>>>>> to compensate for this second-order temperature dependence? TIA!
>>> Looks like frames did you a disservice. It this the page in question?
>>> http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
>>>
>>> If not, then right click on the link in question and open it in
>>> another window to get the correct URL.
>> Thanks, that's the correct page.
>
> What _exactly_ are you trying to do... compensate a diff pair gain
> over temperature?
>
> ...Jim Thompson

Hi Jim - I'm interested in learning more about what methods work best
for compensating the 1/T temperature dependence in the current source
circuit shown about halfway down the page here:
http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html

The simplest method is apparently to use a voltage divider that contains
a resistor with a positive temperature coefficient, but it's not
entirely accurate and only works over a limited temperature range.
Other methods are mentioned (keeping the circuit in a heater, using a
multiplier) but I'd like to know what sort of method the experienced
analog designers here would prefer.
From: Jim Thompson on 9 May 2010 21:00
On Sun, 09 May 2010 18:59:17 -0400, Bitrex
<bitrex(a)de.lete.earthlink.net> wrote:

>Jim Thompson wrote:
>> On Sun, 09 May 2010 01:40:53 -0400, Bitrex
>> <bitrex(a)de.lete.earthlink.net> wrote:
>>
>>> miso(a)sushi.com wrote:
>>>> On May 8, 8:01 pm, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>>>>> John Larkin wrote:
>>>>>> On Sat, 08 May 2010 20:19:15 -0400, Bitrex
>>>>>> <bit...(a)de.lete.earthlink.net> wrote:
>>>>>>> If you put a reference current into the collector of one half of a
>>>>>>> differential pair,
>>>>>> You've lost me already. What do you mean by putting a current into the
>>>>>> collector of a diff pair? Normally one stuffs a current into the
>>>>>> paralleled emitters.
>>>>>> Can you post a schematic?
>>>>>> John
>>>>> Sorry for not being more clear - in the meantime I was able to find a
>>>>> website that has an example of the circuit configuration I am talking
>>>>> about here, figure 3:
>>>>>
>>>>> http://www.uni-bonn.de/~uzs159/
>>>>>
>>>>> It appears from the text the most common way to compensate the 1/T
>>>>> temperature dependence of the circuit is to use a resistor with a
>>>>> positive temperature coefficient in the circuit that provides the
>>>>> control voltage. To make it work well I guess you would want to bind
>>>>> the differential pair to the tempco resistor with some kind of thermally
>>>>> conductive adhesive.
>>>>>
>>>>>
>>>>>
>>>>>> and then take an output current from the collector of
>>>>>>> the other transistor of a differential pair, the output current as a
>>>>>>> fraction of the reference current will be compensated against variations
>>>>>>> of Is. However, because of the dependence of VT on temperature Vbe will
>>>>>>> now have a positive tempco, and the output current as a fraction of
>>>>>>> the reference current will decrease with increasing temperature of the
>>>>>>> pair. I'm wondering what strategies the analog designers here have used
>>>>>>> to compensate for this second-order temperature dependence? TIA!
>>>> Looks like frames did you a disservice. It this the page in question?
>>>> http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
>>>>
>>>> If not, then right click on the link in question and open it in
>>>> another window to get the correct URL.
>>> Thanks, that's the correct page.
>>
>> What _exactly_ are you trying to do... compensate a diff pair gain
>> over temperature?
>>
>> ...Jim Thompson
>
>Hi Jim - I'm interested in learning more about what methods work best
>for compensating the 1/T temperature dependence in the current source
>circuit shown about halfway down the page here:
>http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
>
>The simplest method is apparently to use a voltage divider that contains
>a resistor with a positive temperature coefficient, but it's not
>entirely accurate and only works over a limited temperature range.
>Other methods are mentioned (keeping the circuit in a heater, using a
>multiplier) but I'd like to know what sort of method the experienced
>analog designers here would prefer.

That's where I'm lost. I see no redeeming social value for the
circuit. What will be the ultimate end use? The example seems to be
from someone with less than a full understanding of bipolar
transistors... although maybe he's grasping at making a log
amplifier... and attacking it cattywampus??

I posted a chip circuit here some time ago, can't seem to find it now
(if anyone remembers, tell me what filename I posted it as :-), but
it's gain in dB's was linear with a control voltage. All temperature
compensation on chip, no thermistors.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The only thing bipartisan in this country is hypocrisy
From: Michael Robinson on 9 May 2010 23:16

"Bitrex" <bitrex(a)de.lete.earthlink.net> wrote in message
news:5Yednf5fg-xt1nvWnZ2dnUVZ_rydnZ2d(a)earthlink.com...
> miso(a)sushi.com wrote:
>> On May 8, 8:01 pm, Bitrex <bit...(a)de.lete.earthlink.net> wrote:
>>> John Larkin wrote:
>>>> On Sat, 08 May 2010 20:19:15 -0400, Bitrex
>>>> <bit...(a)de.lete.earthlink.net> wrote:
>>>>> If you put a reference current into the collector of one half of a
>>>>> differential pair,
>>>> You've lost me already. What do you mean by putting a current into the
>>>> collector of a diff pair? Normally one stuffs a current into the
>>>> paralleled emitters.
>>>> Can you post a schematic?
>>>> John
>>> Sorry for not being more clear - in the meantime I was able to find a
>>> website that has an example of the circuit configuration I am talking
>>> about here, figure 3:
>>>
>>> http://www.uni-bonn.de/~uzs159/
>>>
>>> It appears from the text the most common way to compensate the 1/T
>>> temperature dependence of the circuit is to use a resistor with a
>>> positive temperature coefficient in the circuit that provides the
>>> control voltage. To make it work well I guess you would want to bind
>>> the differential pair to the tempco resistor with some kind of thermally
>>> conductive adhesive.
>>>
>>>
>>>
>>>> and then take an output current from the collector of
>>>>> the other transistor of a differential pair, the output current as a
>>>>> fraction of the reference current will be compensated against
>>>>> variations
>>>>> of Is. However, because of the dependence of VT on temperature Vbe
>>>>> will
>>>>> now have a positive tempco, and the output current as a fraction of
>>>>> the reference current will decrease with increasing temperature of the
>>>>> pair. I'm wondering what strategies the analog designers here have
>>>>> used
>>>>> to compensate for this second-order temperature dependence? TIA!
>>
>> Looks like frames did you a disservice. It this the page in question?
>> http://www.uni-bonn.de/~uzs159/expo_tutorial/index.html
>>
>> If not, then right click on the link in question and open it in
>> another window to get the correct URL.
>
> Thanks, that's the correct page.

I can't tell what he's trying to accomplish.


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