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MT8808

ISO-CMOS 8 x 16 Analog Switch Array

Mitel Networks 

ISO-CMOS MT8808

Functional Description

Address Decode

The MT8808 is an analog switch matrix with an array

size of 8 x 8. The switch array is arranged such that

there are 8 columns by 8 rows. The columns are

referred to as the Y inputs/outputs and the rows are

the X inputs/outputs. The crosspoint analog switch

array will interconnect any X I/O with any Y I/O when

turned on and provide a high degree of isolation

when turned off. The control memory consists of a 64

bit write only RAM in which the bits are selected by

the address inputs (AY0-AY2, AX0-AX2). Data is

presented to the memory on the DATA input. Data is

asynchro-nously written into memory whenever the

STROBE input is high and is latched on the falling

edge of STROBE. A logical “1” written into a memory

cell turns the corresponding crosspoint switch on

and a logical “0” turns the crosspoint off. Only the

crosspoint switches corresponding to the addressed

memory location are altered when data is written into

memory. The remaining switches retain their

previous states. Any combination of X and Y inputs/

outputs can be interconnected by establishing

appropriate patterns in the control memory. A

logical “1” on the RESET input will asynchronously

return all memory locations to logical “0” turning off

all crosspoint switches. Two voltage reference pins

(VSS and VEE) are provided for the MT8808 to

enable switching of negative analog signals. The

range for digital signals is from VDD to VSS while the

range for analog signals is from VDD to VEE. VSS

and VEE pins can be tied together if a single voltage

reference is needed.

The six address inputs along with the STROBE are

logically ANDed to form an enable signal for the

resettable transparent latches. The DATA input is

buffered and is used as the input to all latches. To

write to a location, RESET must be low while the

address and data are set up. Then the STROBE

input is set high and then low causing the data to be

latched. The data can be changed while STROBE is

high, however, the corresponding switch will turn on

and off in accordance with the DATA input. DATA

must be stable on the falling edge of STROBE in

order for correct data to be written to the latch.

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