4.0 ANALOG COMPARATOR INPUTS

The dynamic comparator input current is caused by the pe-

riodic switching of on-chip stray capacitances. These are

connected alternately to the output of the resistor ladder/

switch tree network and to the comparator input as part of

the operation of the chopper stabilized comparator.

The average value of the comparator input current varies di-

rectly with clock frequency and with V

IN

as shown in

Figure 6.

If no filter capacitors are used at the analog inputs and the

signal source impedances are low, the comparator input cur-

rent should not introduce converter errors, as the transient

created by the capacitance discharge will die out before the

comparator output is strobed.

If input filter capacitors are desired for noise reduction and

signal conditioning they will tend to average out the dynamic

comparator input current. It will then take on the characteris-

tics of a DC bias current whose effect can be predicted con-

ventionally.

Typical Application

TABLE 2. Microprocessor Interface Table

PROCESSOR

READ

WRITE

INTERRUPT (COMMENT)

8080

MEMR

MEMW

INTR (Thru RST Circuit)

8085

RD

WR

INTR (Thru RST Circuit)

Z-80

RD

WR

INT (Thru RST Circuit, Mode 0)

SC/MP

NRDS

NWDS

SA (Thru Sense A)

6800

VMA

•

φ2•R/W

VMA

•

φ•R/W

IRQA or IRQB (Thru PIA)

DS005672-10

*Address latches needed for 8085 and SC/MP interfacing the ADC0808 to a microprocessor

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