Strange LTP cascoding circuit

roender · 11th June 2007, 07:54 AM

What are the role of D501 and D503 in this schematic?
Have something to do with high tempco of jfet ccs?

AKSA · 11th June 2007, 08:10 AM

Roender,

Compensation..... helps trim OLG to near unity close to the pole.....

Hugh

roender · 11th June 2007, 08:18 AM

Thank you sir Hugh Dean

Can you be more specific, please.
It is hard to believe that 1n4148 diode can be used for frequency compensation

Mihai

AKSA · 11th June 2007, 10:23 AM

Mihai,

My mistake; I apologise, I was thinking of the highlighted capacitor between the LTP collectors!!'

These diodes are used to thermally compensate the BE junctions of TS15 and TS15 since both are fed from a current source and only one of the voltage reference diodes compensates the BE voltage of the CCS.

To be honest, I don't believe they are really necessary, particularly if you replaced the two diodes of the CCS with a green LED, which has almost the same tempco as the be junction of the CCS transistor.

Again, I'm sorry Mihai, I mistook the cap for your question!

Cheers,

Hugh

11th June 2007, 08:10 AM	#2
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Roender, Compensation..... helps trim OLG to near unity close to the pole..... Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

11th June 2007, 10:23 AM	#4
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Mihai, My mistake; I apologise, I was thinking of the highlighted capacitor between the LTP collectors!!' These diodes are used to thermally compensate the BE junctions of TS15 and TS15 since both are fed from a current source and only one of the voltage reference diodes compensates the BE voltage of the CCS. To be honest, I don't believe they are really necessary, particularly if you replaced the two diodes of the CCS with a green LED, which has almost the same tempco as the be junction of the CCS transistor. Again, I'm sorry Mihai, I mistook the cap for your question! Cheers, Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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11th June 2007, 08:18 AM	#3
roender diyAudio Member Join Date: Sep 2006	Thank you sir Hugh Dean Can you be more specific, please. It is hard to believe that 1n4148 diode can be used for frequency compensation Mihai

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