ADS4145: ADC and amplifier

Hello Gareth, 

  LMH6518 is a good suggestion. This device can support the bit range and Gsps ADCs. It also has integrated output voltage clamping at each internal stage of the device. The common-mode can be shifted below 1.2V to 0.95V for ADS4145 if needed as explained on page 29-30 of the LMH6518's datasheet. 

  The main issue is that the LMH6518 will not be able to support 2Vpp Full Scale (FS) range of the ADS4145. It can support up to 1.8Vpp differentially, but it is recommended to stay within 800-900mVpp range for better linearity and distortion performance. In this case, the ADC can be switched or the VGA/PGA to LMH6881 or THS770012.

  Is the customer's application within oscilloscope front end domain? I can move this thread over to our high speed ADC team so they can give suggestions and advice on the ADC end of the design.

Thank you,
Sima 

Hi Sima

Thank you for your help.

The customer's application is in the field of oscilloscopes

could you help provide more product information on amplifiers,

DAC and ADC in the field of oscilloscopes 

Hello Gareth,

  For general oscilloscope information, we do have the BUF802 which is specifically useful for oscilloscope front end applications. This wideband buffer offers high input impedance and low noise as a front-end amplifier. 

  But, in this specific application I believe any of the above discussed variable gain amplifiers would satisfy the customer's requirements. 

1. LMH6881
2. LMH6517
3. LMH6518 (clamping function, but not up to 2Vpp Full Scale) 
4. THS770012

  The above are all 5V single supply variable fully differential amplifiers. If you would need to adjust the common-mode voltage lower than 2.0V/2.5V, I would suggest adding a unity gain fully differential amplifier such as the LMH6553 (has integrated output clamping) or LMH6552 as a second stage with an ability to adjust the common-mode voltage for improved distortion performance.

   Or, the customer could look into the LMH6401 which is also variable gain amplifier, but with adjustable power supplies for adjusting common-mode output at peak distortion performance. A reference design using this part in a oscilloscope front end design can be found at this link. 

  For ADC side, I have moved this thread to our high speed ADC team. They will give suggestions shortly, and from there the thread will most likely be moved to our DAC team. I will be receiving notifications to this thread if there are follow-up questions to the fully differential amplifier design. 

Thank you,

Sima 

Hi Gareth,

Let me know if you have any ADC questions. Is the customer still interested in the ADS4145?

Regards,

Rob

Hi Ron

Customers are looking for an ADC with 3.3V I/O to replace the ADS4145.
could you please let me know if you have any comments.

Thanks you

Hi Gareth,

Understood on the I/O. Can the customer please share some other details for the converter, number of bits, sampling rate, number of channels, power, any other desired features?

Thx,

Rob

Hi Ron

The customer specification is as follows

It will be easier for us to develop with parallel I/O.

These are the specifications we want to achieve

1. I/O 3.3V  Parallel
2. Resolution：12~14bit
3. Bandwidth：more than 30MHz (include LNA and VGA/PGA)
4. sampling rate：100MHz~125MHz per channel.
5. 2 channels
6. Suitable for LMH6518SQE