Small signal toggle switch

[Hawaka]

Hello,

I'm currently building a small signal amplifier. In order to make it more more useful, I would like to have switchable gain stage (On/Off). It will be battery powered, BW around 2MHz.

Is there a good alternative to small signal relay, such as a mechanical toggle switch?

[CaptDon]

When you say band width 2 MHz are you speaking of a D.C. to 2 MHz signal or a signal 2 MHz wide at some base frequency like 10 MHz? A single D.P.D.T. toggle switch may work fine for you. Pay careful attention to grounding the coax or shielded signal wires near the switch to reduce signal leakage. On the center pins of the switch, on side goes to your input connector and the other side to your output connector. In one position of the switch you wire a little jumper so the input directly bridges to the output. In the other position the switch will feed your amplifier from the input side and route the amplifier output to the output side of the switch. I have seen average quality D.P.D.T. switches used in attenuator circuits on commercial products up to at least 10 MHz. Of course a fully shielded coax type switch may be required if you have over 40 Db of gain since without proper shielding you may have self oscillation problems.

[Hawaka]

DC to 2MHz

The question is more like would one of these usual toggle switches be good enough for routing the signal either into the gain stage or bypass it? Would wetting current or frequency BW be an issue?

[David Hess]

DC to 2MHz

The question is more like would one of these usual toggle switches be good enough for routing the signal either into the gain stage or bypass it? Would wetting current or frequency BW be an issue?

A small printed circuit board mounted switch will be fine up to 2 MHz, but keep the circuit traces short unless they are low impedance.  The switch specifications may say if a wetting current is required, but in my experience switches like that never fail in small signal applications anyway.

[CaptDon]

At the frequencies of interest you could probably use it. If the switch was going to remain in one position for months on end you may develop contact resistance and when switching to the long unused side very poor contact, but simply toggling the switch back and forth about a dozen times should be enough to cure the issue due to the switch having a bit of internal wiping action. I much prefer the mini toggles with the solder tabs to keep signal routing short and using shielded wire right up to the switch.

[ejeffrey]

Simple mechanical switches will probably work fine at 2 MHz.  CMOS analog switches / mutliplexers can go to higher bandwidth but limit your signal range. Those are probably the two most basic options for low speed DC coupled signal switching.