ERICSSON EH238 TechDes

Technical Description

Ericsson Handheld Telephone 1341-B

Technical Description

Contents

Technical Description

Design

Mechanical ______________________________________________6 Electronics ______________________________________________ 6

Functional Overview

Reception _______________________________________________7 Transmission_____________________________________________8 Automatic Frequency Control (AFC)__________________________8 Low Frequency (Audio) Processing___________________________8 Companding _____________________________________________9 Logic___________________________________________________9 Power Supply ___________________________________________9

Functional Blocks and Units Description

Frequency Generation_____________________________________10

Transmitter _____________________________________________12

Receiver _______________________________________________13

Power Supply Monitoring _________________________________14 Power Supply: Charging __________________________________15 Control Logic ___________________________________________15

Audio Processing ________________________________________17

ON/OFF-Button _________________________________________18

________________________________________________6

__________________________________7

____________ 10

VCTCXO____________________________________________10 Rx Frequency Synthesizer_______________________________10 Tx Frequency Synthesizer_______________________________12

Driver Stage_________________ __ __ __ __ __ __ __ __ __ __ __ __ _13 Control of Output Power________________________________13

RF-Stage ____________________________________________13 IF Stage _____________________________________________13

System Interface ______________________________________16 Processor ____________________________________________16 Display _____________________________________________16 Keyboard ____________________________________________16

Audio Circuits in Transmission___________________________17 Audio Circuits in Reception _____________________________ 18

Continued on next page

Technical Description

The Major IC Packages

CARL ________________________________________________ 19

Built-in Microprocessor _______________________________ 19 Serial Port (in Processor) _______________________________ 20 ROM ______________________________________________ 20 RAM ______________________________________________ 20 Clock Generator ____________ __ __ __ __ __ __ __ __ __ __ __ __ _ 20 Modem ____________________________________________ 20 SAT ______________________________________________ 20 BAR Generator ______________________________________ 21 Serial Interface ______________________________________ 21 IF Counter __________________ __ __ __ __ __ __ __ __ __ __ __ _ 21 Ports ______________________________________________ 21 Baud Clock_____________________ __ __ __ __ __ __ __ __ __ __ _ 21

BERTRAM ______ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ __ 22

Serial interface _______________________________________ 22 ADC ______________________________________________ 22 Digital inputs _______________________________________ 22 Digital outputs ______________________________________ 23 DAC ______________________________________________ 23

AFC amplifier ______________________________________ 23 LINA _________________________________________________ 23 Duplex Filter ___________________________________________ 24 EPROM_______________________________________________ 24 EEPROM______________________________________________ 24 Interface Block _________________________________________ 24

______________________________ 19

Technical Description

The Ericsson Handheld Telephone 1341-B is a pock et t ele phone for opera- tion in the ETACS system.

Special features are:

• Telephone-number store for 199 numbers and names (32 digits and 10

characters ea ch ).

• Recall of stored numbers by name or by memory position.

• Dialling area (6 numbers).

• DTMF dialling from keypad or memory.

• Prompts and error messages.

• Automatic electronic lock for outbound calls (four different levels).

• Call duration meter.

• Call charge meter.

• Received signal strength meter.

• Battery capacity meter and low battery warning.

• Easily charge d ba t ter y pa ck .

• Possibility of connecting handsfree equipment when the telephone is vehi-

cle-mounted.

• Keyboard lock.

• Any-key answer when Handsfree equipment is used.

• Local language in menus.

• Preprogrammed Enquiry Number.

• Displayable Emergency Number.

• Auto Retry on "Network Busy".

• Minute Minder.

• Back light selection.

• CLI functi ons.

In car installations, connection of external units, such as further handsets and so on, is done by a 14-pin system connector and an antenna connector in the click-in holder. The click-in holder also contains circuits for hands-free operation, and a chargi n g un i t , whic h pr ov i de s ch argi n g fr om the car batt e ry .

Technical Description

Design

Mechanical

The housing consists of one plastic front cover, internally metallized to stop radio frequency radiation, and one metal rear cover.

A 14-way pin connector is provided for connection of external equipment.

The telephone contains one circuit board, accomodating all circuits for radio communication, logic and audio processing, as well as the keypad and display parts.

The main parts of the telephone are shown below.

Antenna

Battery

Indicator light

Microphone

Beeper

Display

Keypad

Figure 1. The Main Parts of the Telephone

Electronics

The audio/logic section features mainly CMOS circuits.

Five custom-designed LSI chips are used to minimize the number of componets: a Modem and Logic Control chip named CARL (digital), the Radio In- terface chip BERTRAM (analog and digital), the Audio Control chip LINA (an array of audio filters and switches), a PLL chip named CINDY, and a radio chip named RUT.

Functional Overview

Technical Description

External antenna

ANT-SW

Antenna

Tx BP

Circulator

Strip Rx-ANT

Rx BP

935.0125 MHz

Transmitter

980.0125 MHz

RF-Stage

90 MHz

Tx-Mixer

Power Control

Rx-Synthesizer

45 MHz

SM1341EN/OVERVIEW.GEM

Tx-Synthesizer

Radio-Interface

Chip (BERTRAM)

TCXO (14.85 MHz)

44.55 MHz

IF-Block

Discriminator

450 kHz

Voltage

Regulator

MOD

CONTROL BUS

DISCR

Figure 2. Functional Blocks; Radio Board

(Frequencies refer to Channel 1)

Reception

The receiver operates within the frequency band 917.0125 to 949.9875 MHz.

Assuming that channel 1 is active, a 935.0125 MHz signal is received at the antenna and fed to the receiver via the duplex filter (RxBP). The Rx-synthesizer is instructed by the logic to produce a signal with a frequency 45 MHz above the received frequency, in this case 935.0125 + 45.000 = 980.0125 MHz. This signal is phase-locked to the 14.85 MHz reference from TCXO and mixed with the antenna signal. This provides the 45 MHz IF signal:

980.0125 MHz - 935.0125 MHz = 45 MHz.

Technical Description

The IF block receives a 2nd LO frequency signal of 44.55 MHz from BERTRAM (3x14.85 MHz from TCXO). This is mixed with the incoming signal, which provides an output of 450 kHz:

45 MHz - 44.545 MHz = 0.450 MHz = 450 kHz.

The 450 kHz signal is then demodulated and amplified, all within the IF block. Discrimination of the 450 KHz signal and low-frequency filtering is performed by the BERTRAM circuit.

An RSSI-signal block, is used to measure the strength of the radio signal. The measured value is read by an A/D-converter in BERTRAM.

(Received Signal Strength Indicator

), generated in the IF-

Transmission

The carrier frequency for mixer) a fixed value of 90 MHz from the Rx synthesizer frequency, in this case 980.0125 MHz as applies for channel 1. The 90 MHz frequency is generated by the Tx synthesizer and is phase locked to the reference frequency of

14.85 MHz.

980.0125 MHz - 90 MHz = 890.0125 MHz.

After amplification in the tional coupler and the duplex filter (Tx BP). A duplex separation of 45 MHz will thus be obtained; 935.0125 - 890.0125 MHz = 45 MHz. The power delivered out to the antenna is max. 600 mW; six power levels in steps of 4 dB.

transmission

Transmitter

is obtained by subtracting (in the Tx-

block it is fed to the antenna via a direc-

Automatic Frequency Control (AFC)

The frequency control is handled by a special AFC-program. Input to the program is a 450 kHz signal (2nd IF-frequency), which includes information about the base-station frequency and the TCXO-frequency. The report on TCXO frequency permits the program to compensate for temperature changes and possible aging. Prescaling of the 450 kHz frequency down to 54 kHz for AFC and data modem is performed by the BERTRAM circuit.

Low Frequency (Audio) Processing

The main purpose of the audio circuits is to carry out the signal processing that is required to match the audio signal from the microphone to the modulator of the transmitter. Likewise, the signal from the receiver discriminator is processed to suit the earphone. Low frequency processing is performed by an IC package referred to as LINA, including also facilities for the generation of DTMF tones.

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