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.

distortion (INL) problem in sigma delta modulator

Status
Not open for further replies.

you23

Newbie level 3
Joined
Aug 12, 2010
Messages
3
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
japan
Activity points
1,304
Hi,
I designed 2nd order sigma-delta modulator (1bit), and made chip, and measuring now.
I use FPGA after modulator output. the FPGA is used for sinc3 decimation filter (16bit out).


I have a distortion problem for measurement.

test condition;
VDD=3V, VSS=0V, VREF+=3V, VREF-=0V, VCOM=0.4*VDD(from external)
fclk=100k, 250k, 500k from external generator.
I use 16bit DAC and buffer amplifier(VDD=5V, VSS=-5V) for input.
Sweep this DAC level from 0 to VDD. (I checked good result(linerlity) by using other ADC).
Sweep DAC level:
puluse input : 0 to VDD (full scale)
minus input : common (0 or VDD/2 or VDD)

Detail of problem;
No change in fclk(100k to 500k), VDD(2V to 4V), minus input level(0 or VDD/2/ or VDD).
When I change input pulse and minus, I got save result.
I made two chip. these difference is switch size.
one is 1:1 switch (NMOS 2u/1u : PMOS 2u/1u) for all transmission switch.
another is 1:3 switch (NMOS 3u/1u : PMOS 9u/1u) for all transmission switch.
for these chip, INL curve is different. (attach graphes below)
I measured 5 pics for each chip. and these are same trend bud level is a little different.
And This INL does not occur in simulation (BSIM3.22, level 49, HSPICE)
I have not tried post layout simulation, but I inted to care for near hi-impedance lines....

pleasae advice me.
 

Attachments

  • delsig_cir01.JPG
    delsig_cir01.JPG
    47.6 KB · Views: 77
  • SW1.JPG
    SW1.JPG
    45.2 KB · Views: 78
  • SW3.JPG
    SW3.JPG
    40.1 KB · Views: 77

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top