ML2713EH Просмотр технического описания (PDF) - Micro Linear Corporation

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ML2713EH

Radio IF Transceiver

Micro Linear Corporation 

PRELIMINARY

ML2713

FUNCTIONAL DESCRIPTION

INTRODUCTION

The ML2713 is the complete IF section of Micro Linear's

2.4GHz frequency hopping, half duplex transceiver

chipset. The down conversion super-heterodyne receiver

circuits contain an image reject down-convert mixer, a

limiter, a discriminator, a receive data filter and a

tracking A/D converter. The transmit circuits contain a 6-

bit D/A converter to digitally generate the IF, an anti alias

filter and an image reject up-convert mixer. When

combined with the ML2712 it enables design of high

performance 2.4GHz half duplex radios with a fast

switching time between receive and transmit modes. This

is ideal for applications such as frequency hopping radios

based on the IEEE 802.11 FH standard.

The ML2713 has four modes of operation; 1) Filter Align,

2) Transmit, 3) Receive, and 4) Sleep. The operating

modes of the ML2713 can be programmed through a 3 pin

parallel interface.

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. In this way the frequency of the

digitally generated transmit IF is normally designed to

equal the received 2IF, as will be described below. (This

radio architecture allows for a fast receive-to-transmit

switching speed, as no PLLs require re-tuning.) The output

of the 2IF filter is connected to the transmit image reject

up-convert mixer. This 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.

The ML2713 has three filters; the 2IF, discriminator, and

data. Part of each filter is off chip, made up of external

components, and part is on chip. The 2IF and

discriminator filters have external inductors and

capacitors configured to give a bandpass characteristic.

In the Filter Align mode the ML2713 will adjust an on

chip capacitor array that is in parallel with the external

capacitance to correct for any tolerances in the external

components values, thereby centering the bandpass filters

to the correct frequency. In this way any production

trimming of the filters is eliminated. The data filter is

made up of on chip op-amps and off chip resistors and

capacitors and does not need to be aligned or trimmed.

In the Filter Align mode the ML2713 will adjust an on

chip capacitor array that is in parallel with the external

capacitance to correct for any tolerances in the external

components values, thereby centering the bandpass filters

to the correct frequency. In this way any production

trimming of the filters is eliminated. The data filter is

made up of on chip op-amps and off chip resistors and

capacitors and does not need to be aligned or trimmed.

In the Filter Align mode the ML2712 provides an 8MHz

signal to the 2LO port of the ML2713. The 2IF filter will

remove the fundamental of this signal, and pass the third

harmonic at 24Mhz to the limiter and discriminator. This

24MHz should result in a zero signal at the discriminator

output. If it does not, the alignment circuit will adjust the

on chip capacitor array until a zero signal is achieved.

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

236MHz, and the 6-bit D/A converter is driven by a

digitally generated FSK modulated signal from the

baseband chip. Digital generation ensures that the

In the Receive mode, the ML2712 (in typical

applications) drives a 1IF signal of 260MHz through the

SAW filter and into the ML2713's 1IF port, and provides

the same 236MHz signal to the 2LO input as above. The

1IF port gains up the signal to improve the noise figure,

and sends the 1IF signal to the image reject down-convert

mixer. The mixer produces a 260MHz minus 236MHz or

24MHz 2IF signal which is then filtered by the 2IF filter.

This signal is gained up by the limiter stage, and sent to

the discriminator. The discriminator will convert changes

in the 2IF signal into a time varying signal which is then

filtered by the data filter. Increases in the 2IF result in

increasing voltage at the data filter output. The data filter

in turn drives one input of the output comparator. The

other input of the comparator is driven by the 6-bit D/A

converter. If the output of the D/A converter is lower than

the output of the data filter, the comparator output will

drive high. If the output of the D/A converter is higher

than the output of the data filter, the comparator output

will drive low. In this way a tracking A/D whose outputs

are the inputs to the D/A, and which follows the data

filter output, is implemented.

The offset errors of a transmitting source may be removed

by a receiving ML2713 during preamble. During

preamble, the Vdc capacitor can be put in the acquire

mode, and the average level of the data filter output will

appear across it. Once Vdc is put in the hold mode, and

data begins, all levels out of the data filtered are

referenced to the Vdc voltage, thereby removing any

offsets in the data.

In the Sleep mode, all circuits are powered off and the

chip typically draws less than 1mA.

January, 2000 PRELIMINARY DATASHEET

7

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