1.2 VCO FREQUENCY TUNING

The center frequency of the RF VCO is determined mainly

by the resonant frequency of the tank circuit. This tank circuit

is implemented on-chip and requires no external inductor.

LMX2542 actively tunes the tank circuit to the required fre-

quency with the built-in tracking algorithm.

1.3 POWER CONTROL

LMX2542 includes a powerdown mode to reduce the power

consumption. LMX2542 can be powered down when the CE

pin is set LOW, independent of the state of the powerdown

bits. When CE is set HIGH, powerdown is controlled through

the MICROWIRE. The RF and IF circuitries are individually

powered down by setting the RF_EN (R1[3]) and IF_EN

(R2[2]) bits LOW respectively. Refer to Section 2.3.2 and

Section 2.4.1 for details on how to program the RF_EN and

IF_EN bits.

CE Pin

RF_EN

IF_EN

RF

Circuitry

IF

Circuitry

0

X

X

OFF

OFF

1

0

0

OFF

OFF

1

0

1

OFF

ON

1

1

0

ON

OFF

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1

ON

ON

Note:

1. X refers to a don’t care condition.

2. The RF circuitry includes the whole RF synthesizer sys-

tem (synthesizer and VCO).

3. The IF circuitry includes the IF synthesizer block only.

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