LMX2364 datasheet(21/39 Pages) NSC

21 / 39 page

Charge Pump Currents

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The above block diagram shows the test procedure for test-

ing the RF and IF charge pumps. These tests include abso-

lute current level, mismatch, and leakage. In order to mea-

sure the charge pump currents, a signal is applied to the high

frequency input pins. The reason for this is to guarantee that

the phase detector gets enough transitions in order to be

able to change states. If no signal is applied, it is possible

that the charge pump current reading will be low due to the

fact that the duty cycle is not 100%. The OSCinIF Pin is tied

to the supply. The charge pump currents can be measured

by simply programming the phase detector to the necessary

polarity. For instance, in order to measure the RF charge

pump current, a 10 MHz signal is applied to the FinRF pin.

The source current can be measured by setting the RF PLL

phase detector to a positive polarity, and the sink current can

be measured by setting the phase detector to a negative

polarity. The IF PLL currents can be measured in a similar

way. Note that the magnitude of the RF and IF PLL charge

pump currents are also controlled by the RF_CP and IF_CP

bits. Once the charge pump currents are known, the mis-

match can be calculated as well. In order to measure leak-

age currents, the charge pump current is set to a TRI-STATE

mode by enabling the counter reset bits. This is RF_RST for

the RF PLL and IF_RST for the IF PLL.

LMX2364 Datasheet(PDF) 21 Page - National Semiconductor (TI)