SCDA042 May   2022 MUX36D08 , MUX36S16 , TMUX1109 , TMUX1111 , TMUX1112 , TMUX1113 , TMUX1121 , TMUX1122 , TMUX1123 , TMUX6111 , TMUX6112 , TMUX6113 , TMUX6121 , TMUX6122 , TMUX6123 , TMUX7208 , TMUX7209 , TMUX7211 , TMUX7212 , TMUX7213 , TMUX7219 , TMUX8108 , TMUX8109 , TMUX8212

 

  1.   Trademarks
  2. 1What is Guarding?
  3. 2Guarding Best Practices
  4. 3How Can Leakage Affect the Performance of a Precision Application?
  5. 4Multiplexer Recommendations for Precision, Low Leakage Applications

3 How Can Leakage Affect the Performance of a Precision Application?

Leakage currents introduced from multiplexers can contribute to undesirable results when implemented into a high precision application. Table 3-1 shows that there are two different multiplexers to choose from.

Table 3-1 Multiplexer Performance Comparison
Multiplexer Leakage Performance (25C/125C) On-Resistance (25C/125C)
TMUX1108 3pA/950pA 2.5 Ω/4.9 Ω
TMUX1308 1nA/800nA 75 Ω/270 Ω

These devices will have leakage and resistance components to them that can have an influence on the application and contribute error if proper guarding precautions are not put into place. The error that is introduced from these leakage currents is equivalent to the approximate amount shown in Equation 1.

Equation 1. V E R R O R =   R O N +   R S O U R C E   ×   I L E A K

To further clarify, the model of a multiplexer’s ON leakage current is shown in Figure 3-1.

Figure 3-1 ON-Leakage for Multiplexers

When feeding into a high impedance node, the leakage current takes the path of least resistance, which is through the on-resistance and source-resistance path and induce an offset error that affects the measurement at the output. Continuing using the chosen multiplexers above, it is evident that leakage can indeed be significant if proper guarding and device selection is not taken into serious consideration (below is assuming Rsource is negligible).

Table 3-2 Multiplexer Induced Offset Error
Multiplexer Leakage Performance (25°C/125°C) On-Resistance (25°C/125°C) Offset Error (25°C/125°C)
TMUX1108 3 pA/950 pA 2.5 Ω/4.9 Ω 7.5 pV/4.6 nV
TMUX1308 1nA/800 nA 75 Ω/270 Ω 75 nV/216 µV

While this example above showcases how leakage currents can contribute heavily to offset error just based on multiplexer selection, it is important to note that the low leakage performance can only be achieved with a proper layout and guarding implemented.