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00326017.JPG (308602 bytes)00120007.JPG (269662 bytes)Ericsson GA628 Cellphone

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Main PCB rear

The wide gold sections on the board form part of the shielding between the 3 main sections of the unit : Transmitter, receiver, and analogue/digital processing.
The transmit section is on the left, the silver rectangle is the RF (Radio frequency) power amplifier module which drives the antenna.
The centre section is the receiver, containing several large filters which allow the receiver to reject signals outside the required channel. Cellphones use a large number of closeley-spaced channels, so extensive filtering is required. This section also contains a highly accurate crystal oscillator, which is temperature compensated to ensure the transmitter and receiver are tuned exactly to the correct channel, to within a few parts per million.
The rightmost section contains the main processor, flash program memory (1MByte), working RAM (32Kbytes), plus the signal processing circuitry required to interface to the RF (transmitter and receiver) and analogue (speech) sections. The red device top-right is the SIM, a smartcard chip containing the user identity.

Extensive use is made of custom chips, due to the huge production volumes, and some of the components are almost invisibly tiny - most of the resistors measure 0.5 x 1mm.

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Main PCB front

Not much on this side - ringer is top-left, gold contacts below connect to speaker in front cover. Metal can bottom left houses more of the RF circuitry. 8KByte memory device left-centre holds user's stored numbers and option settings. Gold pads on right half of board are keyboard contacts. 


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This board is from an earlier analogue (TACS) Ericsson phone.  The largest component, bottom-left, is the duplexing filter. Unlike digital phones, which rapidly alternate transmission and reception, analogue units transmit and receive at the same time (on different frequencies), and this filter seperates the powerful transmit signal from the very sensitive receiver, which handles signals billions of times weaker than the transmitter. The Flash program memory is 128Kbytes - substantially less than the digital unit, which uses a great deal more software signal processing.

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