This is a design circuit for power amps bias circuit. This circuit can be used to temperature compensate the gate voltage of an LDMOS. The output voltage of this circuit is equal to twice the DS4303's VOUT plus the PNP's VBE. The doubled DS4303 voltage is a low temperature-coefficient voltage source. The PNP's VBE will change approximately +2mV/°C, providing temperature compensation for the LDMOS. This circuit can provide good temperature compensation for the LDMOS, assuming that the PNP is thermally coupled to the LDMOS. This is the figure of the circuit;
This circuit is based on LDMOS DS4303 from MAXIM. To calibrate this circuit, place the expected DS4303 output voltage on the VIN pin, and pull the Adjust signal low to trigger the DS4303 to update its output voltage. Once the DS4303 completes its update, measure the quiescent current using the current sense amplifier, and iterate until the proper bias is reached. The input to the DS4303 should be held static while it is converging to ensure it reaches the proper value.
[Circuit schematic source: MAXIM Application Notes]
This circuit is based on LDMOS DS4303 from MAXIM. To calibrate this circuit, place the expected DS4303 output voltage on the VIN pin, and pull the Adjust signal low to trigger the DS4303 to update its output voltage. Once the DS4303 completes its update, measure the quiescent current using the current sense amplifier, and iterate until the proper bias is reached. The input to the DS4303 should be held static while it is converging to ensure it reaches the proper value.
[Circuit schematic source: MAXIM Application Notes]
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