MAX2510 查看數據表（PDF） - Maxim Integrated

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MAX2510

Low-Voltage IF Transceiver with Limiter/RSSI and Quadrature Modulator

Maxim Integrated 

Low-Voltage IF Transceiver with

Limiter/RSSI and Quadrature Modulator

Table 2. RXIN or RXIN Input Impedance

FREQUENCY

(MHz)

SERIES IMPEDANCE

(Ω)

100

275 - j203

200

149 - j184

300

94 - j143

400

64 - j109

500

53 - j87

Receive IF Filter

The interstage filter, located between the MIXOUT pin

and the LIMIN pin, is typically a three-terminal, 330Ω,

10.7MHz bandpass filter. This filter prevents the limiter

from acting on any undesired signals that are present

at the mixer’s output, such as LO feedthrough, out-of-

band channel leakage, and spurious mixer products.

The filter connections are also set up to feed DC bias

from VREF into LIMIN and MIXOUT through two 330Ω

filter-termination resistors. (See the Typical Operating

Circuit for more information).

Transmit Output Matching

The transmit outputs, TXOUT and TXOUT, are open-

collector outputs and therefore present a high

impedance.

For differential drive, TXOUT and TXOUT are connected

to VCC via chokes, and each side is AC coupled to the

load. A terminating resistor between TXOUT and

TXOUT sets the output impedance. This resistor pro-

vides a stable means of matching to the load.

TXOUT and TXOUT are voltage-swing limited, and

therefore cannot drive the specified maximum power

across more than 150Ω load impedance. This load

impedance typically consists of a shunt-terminating

resistor in parallel with a filter load impedance. To drive

higher output load impedances, the gain must be

reduced (via the GC pin) to avoid saturating the TX out-

put stage.

For single-ended applications, connect the unused TX

output output pin directly to VCC.

400MHz ISM Applications

The MAX2510 can be used as a front-end IC in appli-

cations where the RF carrier frequency is in the

400MHz ISM band. In this case, Maxim recommends

preceding the MAX2510 receiver section with a low-

noise amplifier (LNA) that can operate over the same

supply voltage range. The MAX2630–MAX2633 family

of amplifiers meets this requirement. In many applica-

tions, the MAX2510’s transmit output power is sufficient

to eliminate the need for an external power amplifier.

______________________Layout Issues

A well-designed PC board is an essential part of an RF

circuit. Use the MAX2510 evaluation kit and the recom-

mendations below as guides to generate your own

layout.

Power-Supply Layout

A star topology, which has a heavily decoupled central

VCC node, is the ideal power-supply layout for minimiz-

ing coupling between different sections of the chip. The

VCC traces branch out from this node, each going to

one VCC connection in the MAX2510 typical operating

circuit. At the end of each of these traces is a bypass

capacitor that presents low impedance at the RF fre-

quency of interest. This method provides local decou-

pling at each VCC pin. At high frequencies, any signal

leaking out of a supply pin sees a relatively high imped-

ance (formed by the VCC trace impedance) to the cen-

tral VCC node, and an even higher impedance to any

other supply pin, minimizing Vcc supply-pin coupling.

A single ground plane suffices. Where possible, multi-

ple parallel vias aid in reducing inductance to the

ground plane.

Place the VREF decoupling capacitor (0.1µF typical) as

close to the MAX2510 as possible for best interstage fil-

ter performance. For best results, use a high-quality,

low-ESR capacitor.

Matching/biasing networks around the receive and

transmit pins should be symmetric and as close to the

chip as possible. A cutout in the ground plane under

the matching network components can be used to

reduce parasitic capacitance.

Decouple pins 19 and 21 (VCC) directly to pin 20 (Rx,

Tx ground), which should be directly connected the

ground plane. Similarly, decouple pin 8 directly to pin 7.

Refer to the Pin Description table for more information.

______________________________________________________________________________________ 11

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