AD9561JR 데이터 시트보기 (PDF) - Analog Devices

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AD9561JR

Pulse Width Modulator

Analog Devices 

ANALOG DEVICES FAX-ON-DEMAND HOTLINE - Page

AD9561

This yields the maximum time from the trailing edge of CAL IN

to the rising edge ofCAL OUT. As an example, the maximum

time required for auto-calibration for a system with clock ITequency

of 20 MHz is 102.4 ms plus the width of the CAL IN pulse.

Power Reduce

The POWER REDUCE function permits the user to power

down all nonessential circuits when the printer is not active.

Applying a Logic "0" to POWER REDUCE decreases the

power supply requirement by approximately half.

An ideal transfer would give 0% (or 0 ns) pulse width for a Code O.

As the code is incremented in steps of one, the pulse width would

increaseby 0.39%untilit reached 100%for Code255.

When operating at high clock rates, several of the most narrow

pulses do not reach valid logic Level" 1" because of finite rise

time. For example, at 20 MHz, a 1.95% pulse (code 5 or 05H)

would have an expected pulse width of I ns. Because the rise

time is typically 1.5 ns, this pulse will not reach a full output

level. Therefore, depending on the clock rate, the lowest set of

APPLICA nONS

DATA Timing

Input DATA to the AD9561 is double latched. As a result of the

codes produces a series of triangle waves increasing in width

and amplitude until a pulse of approximately 3 ns-5 ns reaches

a proper logic level. Thus, the transfer is flat until about

3 ns-5 ns pulse width (number of codes varies as a function of

internal timing, the OUTPUT is delayed more than one clock

CLOCK fi"equency).

period ITomits corresponding DATA word. Figure 6 illustrates

timing of DATA and CONTROL inputs relative to the CLOCK.

A\ CLOCK

O / \ SETU-P.J/I r- HOLD \

DATA

B CONTROL

Because of the new ramp topology in the AD9561, the transfer

function extends slightly greater than 100% (typically 102%) of

the clockperiod. This has the effect of creating smooth transitions

at the CLOCK period boundaries instead of the discontinuities

produced by the AD9560.

SO 4- Figure 6. DATA and CONTROL Timing

The DATA and CONTROL inputs to the AD9561 are stan-

L dard master-slave latches. Inputs are latched in on the rising

/ / / / / ,/\ \ \ \ \X:;:: \L edge of the CLOCK with 2 ns Set-Up time and 2 ns Hold time.

E This is a design improvement over the AD9560 meant to

T simplifYinterfacing the AD9561 to digital processing circuits.

E A propagation delay exists between the CLOCK and OUTPUT

I:=-IcLOCK j-IcLOCK

IcLOCK~

Y

LEM

(RIGHT JUSll FIED}

TEM

DEM

(LEFT JUSTIFIED) (CENTERJUSllFIED)

Figure 8. Dot Clock Period Transitions

pulses. The minimum propagation delay can be observed when As shown in Figure 8, a Leading Edge Modulated pulse folJowed

alternating between codes 0 (OOHhexadecimal) and 255 (FFH

by a Trailing Edge Modulated pulse will stay high ITomthe rising

hexadecimal). This delay is due in part to normal circuit

edge of the first pulse to the falling edge of the second. This is

propagation; the remainder is due to time required to imple-

ment the proprietary ramp function. OUTPUT pulse transi-

due to Code 255 being designed to be typically 102% of the

CLOCK period. (Dashed lines indicate where transitions

tions will typically occur 22 ns after the rising edge of CLOCK. would occur if the code for the following or preceding period

It may vary from 10 ns-35 ns over temperature.

were 0.) Likewise, no gap occurs for maximum width Trailing

Transfer Function

Output pulse width increases with increasing DATA values. As

the heavy line of Figure 7 shows, the transfer function of the

AD9561 is slightly nonideal.

100

Edge Modulation to max pulse width for Dual Edge Modula-

tion. Because the ending and starting characteristics of all

modes are symmetrical, any combination of pulses that ends at

the boundary of the first period and starts at the boundary of

the second period will produce a continuous pulse across the

boundary.

For the purposes of printing text, or any time absolute white or

80

black is required, 0 is decoded and a 100% LOW is output in

E

the next CLOCK cycle. Similarly, 255 is detected and the next

eI:

tJ,.: 60

!:i

pulse is 100% HIGH.

Retrace

The RETRACE function permits driving the output to a

;w: 40

constant Logic High. For laser printer applications, applying a

~

logic" 1" to RETRACE holds the laser on during the retrace

~

20

period so end of scan can be detected. Returning it to Logic

Low gives control back to the input data bits DO-D7.

128

255

CODE

Figure 7. Pulse Width Transfer Function

-6-

REV. 0

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