LMX2471 Datasheet, PDF (15/36 Pages) National Semiconductor (TI) – 3.6 GHz Delta-Sigma Fractional-N PLL with 1.7 GHz Integer-N PLL

Bench Test Setups
CHARGE PUMP CURRENT MEASUREMENT PROCEDURE
20072169
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 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 current, a 10 MHz signal is applied to the FinRF pin.
Current Test
RF Source
RF Sink
RF TRI-STATE
IF Source
IF Sink
IF TRI-STATE
RF_CPG
0 to 15
0 to 15
X
X
X
X
RF_CPP
0
1
X
X
X
X
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_CPG and IF-
_CPG bits. Once the charge pump currents are known, the
mismatch can be calculated as well. In order to measure
leakage 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. The
table below shows a summary of the various charge pump
tests.
RF_CPT
0
0
1
X
X
X
IF_CPG
X
X
X
0 to 1
0 to 1
X
IF_CPP
X
X
X
0
1
X
IF_CPT
X
X
X
0
0
1
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