Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Bandgap Voltage Reference Cascode

Status
Not open for further replies.
C

cr4zypt

Newbie level 4
Joined
Feb 25, 2015
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
48
Hello ppl,

I have a question here.

b1.pngb2.png

Can you guys please explain the purpose of the EXTRA top three PMOS (left image)!
Is it to increase estability of the circuit since ampop input terminals are switched on both images?
Shouldn't the extra 3 pmos decrease the amount of control de ampop has on the current mirror?

Because I simulated both circuits under an ideal opamp and the result is nearly the same! The difference is only a few mV at Vref.

Thanks.
 

The cascoding is for PSRR particularly, although the higher
gain (from higher Rout) may make a small difference in the
setpoint voltage and tempco (not much, since Rout is
dominated by the diodes' operating point conductance).
Cascoding kills the lambda current-match errors you'd get
in a simple mirror.
 

The thing is that those PMOS transistors are opeating in Triode region, and their Vds is nearly 0 all the time! So, do they serve their purpose of increasing PSRR at all?
NOTE: Every transistor as the same size.
 

cr4zypt said:
The thing is that those PMOS transistors are opeating in Triode region, and their Vds is nearly 0 all the time! So, do they serve their purpose of increasing PSRR at all?
NOTE: Every transistor as the same size.
Click to expand...

Those PMOS transistors need to be in active region. Else even the current mirroring won't be accurate at all and you can forget about PSR, etc.
You would need to correct the design and keep them in active.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top