About pipeline adc--Sub-adc

[leokaven]

Hi! friend

I'm begin study pipeline adc architecture
I met a problem anybody can help me?please!
Pipeline adc have 1.5bit and 2bit sub-adc

1.5 bit sub-adc need Vref between +1/4Vref and -1/4Vref
2 bit sub-adc need Vref between +1/2Vref, 0 and -1/2Vref
How can i produce these voltage reference?

Sorry!my English is poor
Thanks for your help

 

[gevy]

Usually pipeline ADC is completely differential circuit and reference voltage is differential also.

 

[leokaven]

Thanks for gevy ^^
But how to completely?
1.5 bit sub-adc need Vref between +1/4Vref and -1/4Vref
2 bit sub-adc need Vref between +1/2Vref, 0 and -1/2Vref

I'm read IEEE paper, A 10b 20Msamples/s analog to digital converver, P354
"each core stage contained an ADSC and DAC that shared a common resistor string, the resistor determine the ADSC decision"

I don't know how to completely 1.5bit and 2bit circuit
How many resistor i need in 1.5bit and 2bit sub-adc?

Please help me,friends

 

[chency]

Thanks for gevy ^^
But how to completely?
1.5 bit sub-adc need Vref between +1/4Vref and -1/4Vref
2 bit sub-adc need Vref between +1/2Vref, 0 and -1/2Vref

I'm read IEEE paper, A 10b 20Msamples/s analog to digital converver, P354
"each core stage contained an ADSC and DAC that shared a common resistor string, the resistor determine the ADSC decision"

I don't know how to completely 1.5bit and 2bit circuit
How many resistor i need in 1.5bit and 2bit sub-adc?

Please help me,friends

you should use a refernce , some resistances to divided the voltage, 3k--2k--3k or so ....

 

[leokaven]

HI!chency
Thank for you reply my question!

This is my 1.5bit and 2bit schematic
use fully differential signal ±Vin and ±Vref
if ±Vref=1, I need to produce those are voltage reference
Can i use this schematic?
Are these schematic correct or incorrect?

Thanks for your help!

 

[sigmadelta]

Vref=1
V1=0.9625 V2=0.7125
V3=1.0875 V4=0.8375
these voltages can be produced simply by the resistor ladders
use a simple substractor base on capacitors
V1-V2=0.25=1/4 Vref
V4-V3=-0.25=-1/4Vref
the resistor ladders are also used to produce common voltage
this is how i design the requested ref voltage

 

[Btrend]

HI!chency
Thank for you reply my question!

This is my 1.5bit and 2bit schematic
use fully differential signal ±Vin and ±Vref
if ±Vref=1, I need to produce those are voltage reference
Can i use this schematic?
Are these schematic correct or incorrect?

Thanks for your help!

hi,
the 2bit section is correct, but the 1.5bit is not,
u can check it in the attachment.

 

[chency]

hi,
the 2bit section is correct, but the 1.5bit is not,
u can check it in the attachment.

Btrend is right, but I don't known ,why did you connect gnd! in your circuit? as a diff input flash adc, i think it's no use.

 

[leokaven]

HI!Btrend, sigmadelta and chency
Thank for you reply my question!

I have two way to produce voltage reference in overall circuit
One way, Maybe i can shared a common resistor string determine resistor value produce these voltage reference
for 1.5bit and 2bit sub-adc (fig 1)
My sub-adc(flash adc) is use fully comparator,should i connect gnd in common resistor string ?
Is this schematic correct ?


Another way, connect 2bit sub-adc voltage reference and use in 1.5bit produce it(fig 2)

Thanks for your help!
Sorry!my English is poor

 

[Btrend]

1. the common gnd is the common mode voltage of ur differential input. usually in single rail (0 ~ vcc) application, it is > 0. so in this case u should not connect it to GND. and why u worry about the common gnd ? it is always equal to (+Vref+(-Vref))/2= 0 ....... (ac GND)
2. fig. 1 is correct.
3. but fig.2 is wrong in the generation of +-Vref/2, unless u use some buffer between the right part & left part. or u choose different values of ur resistors

 

[leokaven]

haha~~
I get it!
Thanks for your help!