LTC6946 datasheet(12/30 Pages) LINER

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LTC6946

6946fa

BLOCK DIAGRAM

RF–

GND

MUTE

RF+

VRF

REF–

REFO

≤250MHz

≤100MHz

÷1 TO 1023

÷1 TO 6, 50%

÷32 TO 65535

0.373GHz TO

5.79GHz

MUTE

VREFO

REF+

VREF

R_DIV

LOCK

PFD

O_DIV

N_DIV

B_DIV

CAL, ALC

CONTROL

2.24GHz TO 3.74GHz (LTC6946-1) OR

3.08GHz TO 4.91GHz (LTC6946-2) OR

3.84GHz TO 5.79GHz (LTC6946-3)

TUNE

VVCO

GND

CMA

CMB

CMC

GND

250μA TO

11.2mA

VCP

GND

6946 BD

SERIAL

PORT

STAT

SDO

SDI

SCLK

OPERATION

The LTC6946 is a high performance PLL complete with

a low noise VCO available in three different frequency

range options. The output frequency range may be further

extended by utilizing the output divider (see Available Op-

tions table, for more details). The device is able to achieve

superior integrated phase noise by the combination of

its extremely low in-band phase noise performance and

excellent VCO noise characteristics.

REFERENCE INPUT BUFFER

The PLL’s reference frequency is applied differentially on

pins REF+ and REF–. These high impedance inputs are

self-biased and must be AC-coupled with 470pF capacitors

(see Figure 1 for a simplified schematic). Alternatively, the

inputs may be used single ended by applying the refer-

ence frequency at REF+ and bypassing REF– to GND with

a 470pF capacitor.

A high quality signal must be applied to the REF± inputs as

they provide the frequency reference to the entire PLL. To

achieve the part’s in-band phase noise performance, apply

4.2k

REF+

REF–

4.2k

6946 F01

1.9V

BST

BIAS

VREF

LOWPASS

FILT[1:0]

Figure 1. Simplified REF Interface Schematic

a CW signal of at least 6dBm into 50Ω, or a square wave

of at least 0.5VP-P with slew rate of at least 40V/μs.

Additional options are available through serial port register

h08 to further refine the application. Bits FILT[1:0] control

the reference input buffer’s lowpass filter, and should be

set based upon fREF to limit the reference’s wideband

noise. The FILT[1:0] bits must be set correctly to reach

the LM(NORM) normalized in-band phase noise floor. See

Table 1 for recommended settings.

LTC6946 Datasheet(PDF) 12 Page - Linear Technology

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