8.7 Charge Injection

The TMUX620x devices have a transmission-gate topology. Any mismatch in capacitance between the NMOS

and PMOS transistors results in a charge injected into the drain or source during the falling or rising edge of the

gate signal. The amount of charge injected into the source or drain of the device is known as charge injection,

and is denoted by the symbol QC. Figure 8-7 shows the setup used to measure charge injection from source

(Sx) to drain (Dx).

VDD

VSS

VDD

VSS

0.1 µF

0.1 µF

D

GND

S

SEL

VSEL

VS

VOUT

Output

VD

0 V

3 V

VSEL

QINJ = CL ×

VOUT

tr < 20 ns

tf < 20 ns

CL

Output

Figure 8-7. Charge-Injection Measurement Setup

8.8 Off Isolation

Off isolation is defined as the ratio of the signal at the drain pin (Dx) of the device when a signal is applied to

the source pin (Sx) of an off-channel. The characteristic impedance, Z0, for the measurement is 50 Ω. Figure 8-8

and Equation 2 shows the setup used to measure off isolation. Use off isolation equation to compute off isolation.

GND

S1

D

VSIG

VOUT

50

50

Network Analyzer

VDD

VSS

VDD

VSS

0.1 µF

0.1 µF

VS

Figure 8-8. Off Isolation Measurement Setup

Off−Isolation = 20 × Log  VOUTVS

(2)

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TMUX6201, TMUX6202

SCDS450A – NOVEMBER 2022 – REVISED MARCH 2023

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