THS4522: interface THS4522 to a single ended ADC

Hi Ras,

what ADC are we talking about? It's important...

Kai

A SAR ADC, 12 bit, 2.4 MSPS, Single-Ended

Hi Ras,

Could you give us the part number for this ADC or at least the input RC circuit for the ADC? If so, I can give you a more optimized circuit than by estimating these values from the resolution and sampling rate.

Best regards,

Sean

dear Sean,
thank you for the reply.
i use internal ADC of TMS320F28335 microcontroller.



Best Regards,
Rasool

i access THS4509 for OPAMP also.

Hello Rasool,

I would like some more information in order to help.

1) What is the input signal into the amplifier? I see that the ADC has an input range of 0 - 3V.

2) Why do you want to use a fully differential amplifier rather than shifting the input common mode of a single ended amplifier?

Hi Micah Brouwer,
thank you for replying me.
i have to use these ICs ( THS4509/22) because i access them. these ICs have very high slew rate.
my signal is a fast impulse which rises from 0 to 1 within 10-100 nano seconds.

Regards,
Rasool

Hi Rasool,

I recommend you look at Figure 1 from the THS4522 reference design, found here. www.ti.com/.../sbou080.pdf.
Using a balun, or 1:1 transformer, at the input side is not critical, as long as you hold the output common mode near mid supply, you will stay within the part's input and output voltage range. However, you will likely need to use a balun to convert the differential output signal into the single ended input of the ADC. Simply ground the negative end of the secondary winding and attach the positive end to the ADC. This reference design includes impedance matching also.

Best regards,

Sean

Hi Sean,
thank you for the reply.
is there any technique without a transformer?

Regards,
Rasool

Hi Ras,

You could attach the positive output of the amplifier to the ADC and leave the negative output floating, and the gain will be just be half. If you care more about speed than full scale ADC voltage, use unity gain and a Vocm of 1.5 V. For 0V<Vin<1V, the V+ output will range from 1.5V-2V. Here is some backgound on FDAs you may find useful.

training.ti.com/ti-precision-labs-op-amps-fully-differential-amplifiers-input-and-output-common-mode-and

Best regards,

Sean

Dear Sean,
thank you for the explanation.
but i should and absolutely prefer to use full scale adc voltage.

Regards,
Rasool

thank you Sean.
Regards,
Rasool