Signal
SPDT Analog Switch
Single-pole double-throw analog switching for signal routing.
What is it?
An SPDT (Single-Pole Double-Throw) analog switch is an IC with one common terminal and two switched terminals — logic input selects which switched terminal connects to the common. Unlike a logic gate, SPDT switches pass analog signals bidirectionally (input or output, either way). Used wherever you need to route one signal between two destinations or pick one of two sources to feed downstream.
When do you need it?
- Routing one ADC input between two sensors.
- Selecting between two audio sources to feed an amplifier.
- Switching crystal oscillator outputs to different paths.
- Antenna selection (RF SPDT for 2.4 / 5 GHz dual-band).
- Bypassing a circuit element (e.g., enabling/disabling a filter).
How to pick the right one
- Bandwidth
- How fast a signal can pass through. Standard analog SPDTs: 50-100 MHz. RF-optimised: GHz range.
- RON (on-state resistance)
- Lower = less signal attenuation and lower noise. <1 Ω for high-fidelity audio.
- RON flatness
- How constant RON is across signal voltage. Important for low-distortion analog routing.
- Off-isolation
- How well the off-channel is isolated from the on-channel. Critical for adjacent-channel interference in RF / video.
- VCC range
- Single-supply (1.8-5.5 V common) or dual-supply for bipolar signal handling.
What Magnias offers
Magnias SPDT analog switches target audio, low-frequency signal routing, and small-signal selection in SOT-23-6 / SOT-363 packages. Variants for low-RON audio and general-purpose digital signal switching.
Common questions
SPDT switch vs MUX?
An SPDT is a 1-of-2 multiplexer. A larger MUX is 1-of-4, 1-of-8, etc. Pick SPDT when you only have two sources; pick MUX when you have more.
Can an SPDT switch handle 50 Ω RF signals?
Depends on the part. Standard CMOS SPDTs are not RF-optimised — use them for audio / low-MHz. RF-specific SPDTs are explicitly characterised for 50 Ω impedance match and GHz bandwidth.
Why is RON flatness important?
If RON varies with signal voltage, the switch adds harmonic distortion to the passing signal. Flat RON over the signal range keeps audio THD low and ADC linearity high.