MT8804AP datasheet(3/6 Pages) MITEL

3 / 6 page

CMOS

MT8804A

3-5

Functional Description

The MT8804A is a CMOS/LSI 8 X 4 Analog Switch

Array incorporating an 8 X 4 analog switch array,

address decoder, control memory, and digital logic

level converter.

The analog switch array is arranged in 8 rows and 4

columns. The row input/outputs are referred to as

Lines (L0-L7) and the column input/outputs as

Junctors (J0-J3). The crosspoint analog switches

interconnect the lines and junctors when turned “ON”

and provide a high degree of isolation when turned

“OFF”. Interchannel crosstalk is minimal despite the

high density of the analog switch array. The control

memory of the MT8804A can be treated as an 8

word by 4 bit random access memory. The 8 words

are selected by the ADDRESS (A0-A2) inputs

through the on chip address decoder. Data is

presented to the memory via the four DATA inputs

(D0-D3). This data is asynchronously written into the

control memory whenever the ADDRESS ENABLE

(AE) input is HIGH. A HIGH level written into a

memory cell turns the corresponding crosspoint

switch “ON” while a LOW level causes the crosspoint

to turn “OFF”.

Only the crosspoint switches corresponding to the

addressed memory word are affected when data is

written into the memory. The remaining switches

retain

their

states.

establishing

appropriate patterns in the control memory, any

combination

lines

and

junctors

may

interconnected. A HIGH level on the MASTER

RESET (MR) input returns all memory locations to a

LOW level and turns all crosspoint switches “OFF”

effectively isolating the lines from the junctors. The

digital logic level converters allow the digital input

levels to differ from limits of the analog levels

switched through the array. For example, with

Figure 3 - On Resistance vs. Temperature

(Input Signal Voltage=Supply Voltage/2)

VDD=5V, VSS=0V and VEE=-6V, the control inputs

can be driven by a 5V system while the analog

voltages through the crosspoint switches can swing

from +5V to -6V.

Figure 4 - On Resistance vs. Input Signal Voltage

Figure 5 - 8 x 8 Analog/Digital Switch

8x8 Analog/Digital Switch

Two MT8804s configured as shown, implement

an 8 x 8 analog/digital switch. The switch capacity

can be expanded to an M x N array of inputs/

outputs. Expansion in the M dimension is as

shown

with

the

MT8804A

lines

(L0-L7)

commoned. Expansion in the N dimension is

accomplished by replicating the circuit shown and

connecting the MT8804A junctors (J0-J3) in

common. The address and data control inputs of

the MT8804A’s can be connected in common for

any size and switch provided that the address

enable (AE) inputs are driven individually. A

particular signal path is connected by setting up

the appropriate signals or the address and data

lines and

taking

the corresponding

address

enable input high. The master reset (MR), when

taken high, disconnects all signal paths.

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