Rainbow-electronics MAX2442 Manual do Utilizador descarregar pdf (Página 11)

Oscillator-Tank PC Board Layout

The parasitic PC board capacitance, as well as PCB

trace inductance and package inductance, can affect

oscillation frequency, so be careful in laying out the PC

board for the oscillator tank. Keep the tank layout as

symmetrical, tightly packed, and close to the device as

possible to minimize LO feedthrough. When using a PC

board with a ground plane, a cut-out in the ground

plane (and any other planes) below the oscillator tank

will reduce parasitic capacitance.

Using an External Oscillator

If an external 50Ω LO signal source is available, it can

be used as an input to the TANK or TANK pin in place

of the on-chip oscillator (Figure 3). The oscillator signal

is AC coupled into the TANK pin and should have a

level of about 0dBm from a 50Ω source. For proper

biasing of the oscillator input stage, TANK and TANK

must be pulled up to the V

supply via 50Ω resistors.

If a differential LO source such as the MAX2620 is

available, AC couple the inverting output into TANK.

MAX2440/MAX2441/MAX2442

900MHz Image-Reject Receivers

______________________________________________________________________________________ 11

MAX2440/MAX2441/MAX2442

MAX2440

MAX2441

MAX2442

TANK

50Ω

EXT LO

EXTERNAL LO LEVEL IS

0dBm FROM A 50Ω

SOURCE.

BLOCK

0.01µF

TANK

Figure 3. Using an External Local Oscillator

TRANSISTOR COUNT: 2802

MAX2440

MAX2441

MAX2442

TANK

1/2 D1

VTUNE

TANK

Figure 4. Series Coupled Resonant Tank for Wide Tuning Range and Low Phase Noise

Chip Information

1 2 ... 6 7 8 9 10 11 12

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