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SN74LVC1G3157: SN74LVC1g3157 dB loss

Ray Buck
Prodigy 200 points
Part Number: SN74LVC1G3157
Other Parts Discussed in Thread: TMUX1248, , TS5A3159

What is the dB loss through the switch? There is nothing in the data sheet that gives this information. Normally there would be a curve showing the loss vs frequency. The data sheet says input a signal with a 0.4V bias applied and increase frequency until the -3dB point is observed. This is not acceptable as I do not have a part on hand. I am considering using it, but without the loss figure I will have to rule it out.

I plan to use the device from 1-30 MHz.

  • 0
    TI__Genius 10974 points

    Hi Ray,

    Since this device has a rated bandwidth of 340MHz, using this in an application that uses a 30MHz signal is well within the operating bandwidth of this device and there would be minimal to no attenuation of the signal you are passing.

    If you require such a figure, we also offer the TMUX1248 which has the same configuration, pinout, and functionality as the SN74LVC1G3157 that can be used instead.

    Let me know if you require further assistance on this.

    Thanks!

    Bryan

  • 0 in reply to Bryan Marshall
    Prodigy 200 points

    Bryan,

    Thank you for the quick response. I would like your additional input thoughts on the part. I think you are saying I do not need an amplifier stage after the switch to make up for losses as there are none at 30 MHz. A 30 MHz signal is 8.8% of 340 MHz.

    The reason I question that is I have previously used the TS5A3159B switch which has a 100 MHz bandwidth. Applying the 8.8% number to the TSA3159 means that at 8.8 MHz I would have 0 dB loss through the switch. However, Figure 8 in the data sheet shows roughly 4.5 dB loss through the switch.

    Are you sure the SN74LVCg3157 has no loss at 30 MHz? Has this been tested for confirmation? Maybe the 3157 is a different fabrication process?

  • +1 in reply to Ray Buck
    TI__Genius 10974 points

    Hi Ray,

    There will be some loss, however, it will not be due to frequency. The losses at lower frequencies will be entirely dictated by the on-resistance of the switch as well as any series resistance in the path. In your TS5A3159 example, the -4.5dB at lower frequencies is mostly due to the 50ohm resistor that is used during the testing of this parameter (there is 50 ohms impedance matching during this test to reduce reflections at higher frequencies). The nominal resistance of the TS5A3159 is 1 ohm so the voltage losses will be proportional to that resistance times the current through the path. With the case of the SN74LVC1G3157, it has a typical resistance of 6 ohms, so at lower frequencies the losses will again be determined by the current through the switch times the resistance.

    Hope this helps clear things up!

    Thanks!

    Bryan

  • 0 in reply to Bryan Marshall
    Prodigy 200 points

    Bryan,

    Thanks for the additional comments. That helps clear up the loss issue. I was going to use the switch between the antenna and the bandpass filter of a receiver. The signal level is in the low microvolt range with no current flow to speak of. So the losses should be minimal.

    To confirm that I will order a few pieces and runs some tests with a 50 ohm load.

    Ray