ML2713CH Ver la hoja de datos (PDF) - Micro Linear Corporation

Número de pieza

componentes Descripción

Fabricante

ML2713CH

Radio IF Transceiver

Micro Linear Corporation 

PRELIMINARY

OPERATIONAL MODES (CONTINUED)

ML2713

TRANSMIT MODE

The transmitter is a Frequency Shift Key (FSK) transmitter

in which the modulating signal is a digitally generated

signal from the baseband chip. This signal in turn is

passed through an anti alias filter, and mixed with an LO

signal to produce a 260MHz 2IF signal which is then

passed to the ML2712. The digitally generated 1st If is

designed to be equal to the received 2IF. Such a radio

architecture allows for rapid switching between receive

and transmit modes because the PLLs and filters don't

need to be re-tuned or aligned with each mode switch.

In the Transmit mode, the ML2712 drives the 2LO port at

236MHz, and the 6-bit D/A converter pins DD5-DD0 are

driven by a digitally generated FSK modulated signal

from the baseband chip. Digital generation ensures that

the transmit modulation can be maximized without

concern for variations over temperature and process that

result from varying a VCO frequency directly. The D/A is

typically driven at 32 MHz, and the fundamental

component is 8MHz. The output of the D/A is connected

to the 2IF filter (which is acting as an anti alias filter)

where the 1st alias, which is 32MHz minus 8MHz or

24MHz, is passed. The 2IF filter connects to a 0/90

degree phase splitter, which in turn connects to the

transmit image reject up-convert mixer. The 2LO port

connects to a 0/90 degree phase splitter, which in turn

drives the other input of up-convert mixer. This phase

splitter output mixes with the 2LO port 236MHz signal,

and produces a 260MHz IF signal, which is sent to the

ML2712. In addition, the transmit signal is passed

through the SAW filter, which acts to select the wanted

alias, remove the unwanted up conversion products, and

perform part or all of the modulation filter functions.

Transmitter Circuits

The main circuits active during the transmit mode are:

2IF of 24MHz. Under these conditions, the image

rejection is typically better than 25dB. This is shown in

Figure 2. The fundamental, at 260MHz, is at least 25dB

greater than the image. The products at 8MHz intervals

are unwanted aliases from the D/A converter.

The differential 2LO input port has a nominal 200-Ohm

impedance. The 2LO port is a low impedance common

base stage such that the 2LO signal is not attenuated by

the parasitic capacitance of the ML2712, ML2713, the

interconnect between them, and their packages. Each

input requires external pull down resistors of 4k to

properly bias them. These resistors are internal to the

ML2712, and do not need to be included if that device is

used.

0

-10

Data

Marker 1

-20

Marker 2

-30

-40

-50

-60

-70

160

180

200

220

240

260

280

300

320

340

360

Frequency (MHz)

Figure 2. Typical Transmit Output Spectrum

6-bit D/A Converter

The D/A converter on the ML2713 is a parallel interface,

binary weighted D/A converter, with non-latched CMOS

compatible inputs. The D/A can be driven at frequencies

up to 40MHz.

2IF Filter

The 2IF filter is an off chip inductor and capacitor filter

which is shared between the receive and transmit

circuits.

IF Up-Converter

The image reject transmit mixer consists of a 2IF input 0/

90 degree splitter, 2LO input buffer a 2LO 0/90 degree

splitter, two mixers and an output combiner. The 0/90

degree networks are passive and internal to the IC. The

mixer performs optimally with a 1IF of 260MHz, and a

10

PRELIMINARY DATASHEET January, 2000

Share Link: