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TLV333, what is the chopper frequency and influence to the performance.

Other Parts Discussed in Thread: TLV333

Dear Specialists,

My customer is considering TLV333.

He is some questions about chopper frequency.

Could you please advise?

(1) What hertz is the chopping frequency?

According to the datasheet, 8.3.3 Internal Offset Correction, it says that `This amplifier is zero-corrected every 8 μs using a proprietary technique.`

I thihk It means chopping frequence is 125kHz. Is it right?

(2) How does the chopping frequency influences the characteristics of the device? 

Could I see wideband voltage noise vs. frequency spec. (for example from 0.1Hz to 1MHz)

(3) Is there any limitation of usable frequency?

Generally, usable frequency of chopper amp is small enough  for the chopping frequency.

Do you have any guideline?

I appreciate your great help.

Best regards,

Shinichi

  • Shinichi-san,

    Please see my answers to your questions:

    He is some questions about chopper frequency.

    Could you please advise?

    (1) What hertz is the chopping frequency? The TLV333 chopping frequency varies between devices, and for a given device with temperature and supply level. One-hundred, twenty-five kHz is on the low end for the device and it can actually be about 3x higher for other devices under different temperature/supply conditions. But the variation of the chopping frequency isn't an issue because the sync filter, that filters it and its harmonics, is synchronized with the chopping frequency. 

    According to the datasheet, 8.3.3 Internal Offset Correction, it says that `This amplifier is zero-corrected every 8 μs using a proprietary technique.`

    I thihk It means chopping frequence is 125kHz. Is it right? The 125 kHz is about right on the low end.

    (2) How does the chopping frequency influences the characteristics of the device? The built-in sync filter is very effective in eliminating the clock frequency and harmonics within the TLV333 operating bandwidth.

    Could I see wideband voltage noise vs. frequency spec. (for example from 0.1Hz to 1MHz) Figure 16 in the datasheet shows the voltage and current noise spectral densities from 1 Hz to 10 kHz. We don't have it for 0.1 Hz to 1 MHz. A chopper amplifier doesn't exhibit the 1/f noise characteristic of conventional op amps so the noise below 1 Hz will be almost exactly the same at 0.1 Hz. Above 10 kHz the voltage noise density begins to show some increase, but then the graph cuts off.

    (3) Is there any limitation of usable frequency? Generally, usable frequency of chopper amp is small enough  for the chopping frequency. Do you have any guideline?

    Datasheet Figure 2 shows the open-loop gain (Aol)  vs. frequency plot for the TLV333. You want to make sure that you always have at least 40 dB of loop gain, preferably more, at the maximum frequency associated with the application. For example, the Aol at 1 kHz looks to be a around 50 dB. Therefore, with a loop gain of 40 dB, 10 dB of closed-loop gain can be supported at 1 kHz.

    Regards, Thomas

    PA - Linear Applications Engineering

  • Dear Thomas

    Thank you for your prompt reply and polite advice.

    I am going to send it to the customer.

    I appreciate your great help.

    If the customer has an additional question, I will consult you.

    Best regards,

    Shinichi