LMX2487E Datasheet, PDF (13/47 Pages) Texas Instruments – Low-Power Dual PLLatinum Frequency Synthesizers

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7 Parameter Measurement Information
7.1 Bench Test Set-Ups
7.1.1 Charge Pump Current Measurement
10 MHz
Signal Generator
Semiconductor
Parameter
Analyzer
SMA Cable
SMA Cable
LMX2487E
SNAS404B – MAY 2007 – REVISED JANUARY 2016
DC
Blocking
Capacitor
Frequency
Input Pin
CPout
Pin
Device
Under
Test
OSCin
Pin
Power Supply
Evaluation Board
Figure 18. Charge Pump Current Measurement
Figure 18 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 ensure 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
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 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
Table 4. Charge Pump Test Programming
RF_CPP
0
1
X
X
X
X
RF_CPT
0
0
1
X
X
X
IF_CPP
X
X
X
0
1
X
IF_CPT
X
X
X
0
0
1
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