ADG819_switching current

Document created by analog-archivist Employee on Feb 23, 2016
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I have a question regarding the Ioff current of this device. I wonder if I can
get some help here.
I set VDD = 5V and float pin D. Then I measure current from pin S1 and S2
separately. When I applied 1 or 0 to pin IN, the currents measured from both S1
or S2 are less than 1nA. However when I applied periodic 1 and 0 signal with a 
frequency of 100 kHz (IN changes between 1 and 0 at a frequency of 100 kHz),
the currents measured from S1 and S2 jumped up to uA to 10 uA. I wonder if this
is expected.
Meanwhile, I wonder if you have any switch with spects similar to ADG819 but
with Ioff on the order of nA when the switch is on/off at the frequency of 100
kHz.
I get that the test circuit is similar to the test circuit 3 shown in the data
sheet of ADG819 series by swapping pin S and D. The difference is that the
switch is closed and opened periodically. The voltage at the S1 and S2 pins is
0V.  The customer measured the current at D pin by using DC current meter, so
the current should be rms.

 

The additional current measured when the switch is toggled is due to the charge
injection of the switch. Basically, when the switch is toggled some the voltage
from the gate of the MOS transistors that make up the switch is coupling into
the S and D pin though the gate-source/drain capacitance. This is equivalent to
a change in the charge present on the S/D pins which will change the original
leakage current. The charge injection is dependent on the voltage applied to
the S/D pins, but since the current is measured with a DC meter, the toggling
frequency will also affect the measured current as the meter is averaging out
the pulses caused by charge injection.

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