Using DPDT Switch for Negative Inputs and Rectifiers

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Discussion Overview

The discussion revolves around the use of DPDT switches for handling negative inputs in the context of signal processing, particularly for rectification and amplification of sinusoidal signals. Participants explore the implications of using DC offsets and the characteristics of various switching components.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant inquires about the capability of DPDT switches to handle negative inputs and whether a DC offset would allow only positive sinusoidal inputs to be processed.
  • Another participant notes that mechanical DPDT switches can handle signals up to their breakdown voltage, while CMOS mux chips typically operate close to rail voltages, often limited to lower voltage levels.
  • A suggestion is made to use specific chips like the MAX4564 or DG469, which are dual supply SPDT switches, for the application.
  • Discussion arises about the DG469's capability to switch +/- 15V with dual rail supplies, referencing prior use of a similar unit in a different setup.
  • Concerns are raised regarding the availability of certain chips, leading to a search for alternatives with dual supply capabilities for a signal of +/-5V, powered by +/-12V.
  • A question is posed about the significance of on-resistance in selecting switches, with a participant speculating that lower resistance might indicate better performance due to reduced current supply and power dissipation.
  • Another participant clarifies that lower on-resistance results in less power dissipation and voltage drop, especially important for high-speed applications.

Areas of Agreement / Disagreement

Participants express varying opinions on the suitability of different switching components and the implications of on-resistance, indicating that multiple views remain on the best approach for the application.

Contextual Notes

Participants discuss the limitations of specific components and their voltage handling capabilities, as well as the impact of on-resistance on circuit performance, without reaching a consensus on the optimal solution.

Who May Find This Useful

Individuals interested in signal processing, electronics design, and those exploring the use of switches in rectification and amplification applications may find this discussion relevant.

edmondng
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Are there any DPDT switch that can take negative input?
i want to put a sinusoidal as input and use the output to go through a difference amplifier to create a rectifier.

does it work the same if i put a DC offset so i only get positive sinusoidal input to DPDT, and then use the output to go through a difference amplifier? (maybe i need to subtract DC offset to get the equivalent as without no offset?)
 
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A mechanical DPDT will obviously pass anything upto the breakdown voltage.
Otherwise most CMOS mux chips will switch pretty close to the rail voltage, although a lot of high speed ones are made for switching video so only handle 0-1V levels.
 
getting 2 of these max4564 ior dg469 should work i suppose. its a dual supply spdt
thoughts?
 
The DG one claims to switch +/- 15V with the dual rail supplies.
I used a similair single rail DG unit for a double correlated sampling setup once.
 
actually this chip is probably not available, but doing a product search in vishay spdt dual supply yielded quite a number of chips. my signal is +-5v, i'll just supply it with +-12v

another quick question
when selecting, should i care about on resistance for the gate? what is the difference or function between say an on gate of 10ohm and one with 200ohm. lower resistance means less current supply i guess. so lower means better?
 
Lower on resistance means less power dissapated in the chip if you are sending a large current, it also means less voltage drop if the source of your signal isn't a stiff supply.
At high speeds it also means a lower time constant for the circuit.
 

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