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CSD13380F3: Some spikes from FemtoFET during high frequency

Yeong Kang Liew
Prodigy 20 points
Part Number: CSD13380F3

We are constructing a circuit as shown below(please ignore the MAX4166 circuit on the left as we already isolated out from FemtoFET circuit).

VG1 is a function gen to generate a series of pulses to enable/disable FemtoFET while we are injecting a 50mV voltage through VS3, VF2 is where we probe the output.

When the signal frequency from VG1 <500kHz, the output waveform measured still within expectation. However, once the frequency getting higher than 500kHz, we start to see obvious spike from the waveform as shown in oscilloscope.

Even we construct another circuit and the SW is open, we also see some spikes coming out.

My question is,

  1. Is the spike we measured due to the high switching frequency at the gate? because in both cases we are inputting 5Mhz of signal to the FET. 
  2. Do we have any femtoFET or FET which can handle higher frequency?
  • 0
    TI__Mastermind 32405 points

    Hello Yeong,

    Thanks for your interest in TI FETs. The spikes you are seeing may be layout related or there could be coupling from the gate to drain thru Cgd. Also, you need to be careful with probing and minimize the loop between the probe tip and ground which can pick up noise. Our FemtoFETs are optimized for load switch and general (low frequency) switching applications. Although I have seen some customers use these devices at 10's of MHz. Have you looked at the VGS waveform? How are you connecting the signal generator to your board and how does it get to the gate of the FET? I think it will be easier if we move this discussion to regular email. I will send you a follow up email.

    Best Regards,

    John Wallace

    TI FET Applications