The DC level of the Tx Output pin is shifting excessively when I switch the state of the Tx Enable pin. Why is this happening?
A. The CMX589A Tx Output pin DC level doesn’t shift appreciably unless the pin is being loaded. This loading can be caused either by test equipment probes or connected devices. When the Tx section is not powersaved, the Tx Output pin can be in one of two states; enabled and disabled. In the disabled condition, the Tx Output pin is connected to Vbias through a 500kohm internal resistance. Any loading on the Tx Output pin, including “10x” oscilloscope probes, dirty solder connections, or connected devices with low input impedance, will create a voltage divider effect and can cause the DC level on the Tx Output pin to decrease. To prevent any loading of the Tx Output pin, all connections to the Tx Output pin should have very high input impedance. A buffer amplifier is a good way to prevent loading of the Tx Output pin.
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