Frequency
Input Pin
DC
Blocking
Capacitor
Signal Generator
Semiconductor
Parameter
Analyzer
SMA Cable
10 MHz
Device
Under
Test
Evaluation Board
SMA Cable
Power Supply
CPout
Pin
OSCin
Pin
LMX2486
SNAS324 –JANUARY 2006
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BENCH TEST SETUPS
Charge Pump Current Measurement Procedure
The above block diagram shows the test procedure for testing the RF and IF charge pumps. These tests include
absolute current level, mismatch, and leakage measurement. In order to measure 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 OSCin 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, 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 PLL charge pump current is controlled by the RF_CPG bit. Once
the charge pump currents are known, the mismatch can be calculated as well. In order to measure leakage, the
charge pump is set to a TRI-STATE mode by enabling the RF_CPT and IF_CPT bits. The table below shows a
summary of the various charge pump tests.
Current Test RF_CPG RF_CPP RF_CPT IF_CPP IF_CPT
RF Source 0 to 15 0 0 X X
RF Sink 0 to 15 1 0 X X
RF TRI-STATE X X 1 X X
IF Source X X X 0 0
IF Sink X X X 1 0
IF TRI-STATE X X X X 1
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