Driving a differential Input Amplifier

MUSTAFA ERDOGAN

Other Parts Discussed in Thread: LMH6553

I have a 14 bit A/D converter which accepts differential input. However my signal is single ended. SO I decided to use a front end circuit using two op-amps which converts my single ended signal to differential signal. But at this stage op-amps introduce extra noise and distortion due to 2nd and 3rd harmonics. The frequency of my signal is 5MHz. Is there any operational amplifier that you can suggest whose 2nd and 3rd harmonic values are below -70dBc at 5MHz?

Thanks

over 7 years ago

0 Jim Brinkhurst1 over 7 years ago

TI__Mastermind 44680 points

Hi Mustafa

To achieve good HD2 and HD3 performance at 5 MHz you will need to use a fully differential amplifier that has bandwidth of at least a few hundred MHz.

Here is a search that gives a number of potentially suitable devices:

http://www.ti.com/amplifier-circuit/op-amps/high-speed/products.html?pqs=paqs&familyid=72#p89=Fully%20Differential&p480=1;1&p512=500;2500

Many of the device datasheets will have example circuits showing how to convert a single-ended input signal to differential output as needed to drive a differential ADC input. Figure 56 in the LMH6553 datasheet is one example. Figure 28 of the LMH6553 shows the HD2 and HD3 performance versus input frequency for 2Vpp and 200 ohm load.

I hope this is helpful.

Best regards,

Jim B

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Driving a differential Input Amplifier