7.7 Charge Injection

The TMUX722x has 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 7-7 shows the setup used to measure charge injection from source (Sx) to drain (D).

VDD

VSS

VDD

VSS

0.1 µF

0.1 µF

GND

SELx

VSEL

VOUT

Output

VS

0 V

3 V

VSEL

QINJ = CL ×

VOUT

tr < 20 ns

tf < 20 ns

S1

D1

S2

D2

Output

Output

CL

CL

VS

VS

Figure 7-7. Charge-Injection Measurement Setup

7.8 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 7-8

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

GND

S1

D1

VSIG

VOUT

50Ÿ

50Ÿ

Network Analyzer

1BB +OKH=PEKJ = 20 × .KC

8176

85

VDD

VSS

VDD

VSS

0.1 µF

0.1 µF

50Ÿ

Sx/Dx

VS

Figure 7-8. Off Isolation Measurement Setup

TMUX7221, TMUX7222

SCDS444 – FEBRUARY 2023

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