Video switch parameters

AN2472

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1.4

Differential gain and phase

Differential gain and differential phase refer to how the video switch attenuates the signal

differently for inputs biased at various DC levels.

occurring with a smaller differential gain. A lesser variation of on capacitance of a video

switch over various DC biases results in a lower differential phase.

The differential gain and phase are further defined as below:

Differential gain is the percentage error in the magnitude/amplitude change in the analog

output voltage from the analog input voltage when the input is between 0 V and 0.714 V and

the switch is enabled. Load at the output is 150 Ohm. 0 V and 0.714 V represents the DC

offset.

Differential gain is expressed in % error and is calculated as follows:

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dB = G1 (say)

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dB = G2 (say)

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Then Error = E = G2 - G1 (dB)

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% Error in Gain = Differential Gain = 100 * Antilog (E/20)

The differential phase is measured in a similar way from the AC/transient simulation plot.

1.5

Current consumption

There are two parts to the current, one comes from the current consumed by the logic

control circuit and the other is by the switch itself. The supply of the device is only connected

to the logic control part (switch enable and selection). The analog pulsing input video signal

is the other source of voltage to the video switch.

The current consumption of the switch when it is active but not switching is only determined

by the static current through the logic part of the device. When it is switching, the current is

determined by the logic control elements of the switch.

The input voltage source to the switches' drain/source and the load attached at the switch

output determine the current through the switch itself.

During the standby state, the current consumption of the switch drops to very low and is

practically negligible.

1.6

Delay measurements

The delay measurements include the switch turn-on / turn-off times and the propagation

delays. The measurement is done using the load circuit as shown in the datasheet. For the

waveforms and the timing specifications, refer to the STMAV340 datasheet.