HI5735KCB(1998) Просмотр технического описания (PDF) - Intersil

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HI5735KCB
(Rev.:1998)

12-Bit, 80 MSPS, High Speed Video D/A Converter

Intersil 

HI5735

Noise Reduction

To reduce power supply noise, separate analog and digital

power supplies should be used with 0.1µF and 0.01µF

ceramic capacitors placed as close to the body of the

HI5735 as possible on the analog (AVEE) and digital (DVEE)

supplies. The analog and digital ground returns should be

connected together back at the device to ensure proper

operation on power up. The VCC power pin should also be

decoupled with a 0.1µF capacitor.

Reference

The internal reference of the HI5735 is a -1.23V (typical)

bandgap voltage reference with 50µV/oC of temperature drift

(typical). The internal reference is connected to the Control

Amplifier which in turn drives the segmented current cells.

Reference Out (REF OUT) is internally connected to the

Control Amplifier. The Control Amplifier Output (CTRL OUT)

should be used to drive the Control Amplifier Input (CTRL

IN) and a 0.1µF capacitor to analog VEE. This improves set-

tling time by providing an AC ground at the current source

base node. The Full Scale Output Current is controlled by

the REF OUT pin and the set resistor (RSET). The ratio is:

IOUT (Full Scale) = (VREF OUT/RSET) x 16.

The internal reference (REF OUT) can be overdriven with a

more precise external reference to provide better

performance over temperature. Figure 11 illustrates a typical

external reference configuration.

HI5735

(26) REF OUT

-1.25V

R

-5.2V

FIGURE 11. EXTERNAL REFERENCE CONFIGURATION

Outputs

The outputs IOUT and IOUT are complementary current

outputs. Current is steered to either IOUT or IOUT in proportion

to the digital input code. The sum of the two currents is always

equal to the full scale current minus one LSB. The current out-

put can be converted to a voltage by using a load resistor. Both

current outputs should have the same load resistor (64Ω typi-

cally). By using a 64Ω load on the output, a 50Ω effective output

resistance (ROUT) is achieved due to the 227Ω (±15%) parallel

resistance seen looking back into the output. This is the nomi-

nal value of the R2R ladder of the DAC. The 50Ω output is

needed for matching the output with a 50Ω line. The load resis-

tor should be chosen so that the effective output resistance

(ROUT) matches the line resistance. The output voltage is:

VOUT = IOUT x ROUT.

IOUT is defined in the reference section. IOUT is not trimmed

to 12 bits, so it is not recommended that it be used in

conjunction with IOUT in a differential-to-single-ended appli-

cation. The compliance range of the output is from -1.25V to

0V, with a 1VP-P voltage swing allowed within this range.

TABLE 2. INPUT CODING vs CURRENT OUTPUT

INPUT CODE (D11-D0)

1111 1111 1111

IOUT (mA)

-20.48

IOUT (mA)

0

1000 0000 0000

-10.24

-10.24

0000 0000 0000

0

-20.48

Settling Time

The settling time of the HI5735 is measured as the time it

takes for the output of the DAC to settle to within a 1/2 LSB

error band of its final value during a full scale (code 0000...

to 1111.... or 1111... to 0000...) transition. All claims made by

Intersil with respect to the settling time performance of the

HI5735 have been fully verified by the National Institute of

Standards and Technology (NIST) and are fully traceable.

Glitch

The output glitch of the HI5735 is measured by summing the

area under the switching transients after an update of the

DAC. Glitch is caused by the time skew between bits of the

incoming digital data. Typically, the switching time of digital

inputs are asymmetrical, meaning that the turn off time is

faster than the turn on time (TTL designs). Unequal delay

paths through the device can also cause one current source

to change before another. In order to minimize this, the Inter-

sil HI5735 employes an internal register, just prior to the cur-

rent sources, which is updated on the clock edge. Lastly, the

worst case glitch on traditional D/A converters usually occurs

at the major transition (i.e., code 2047 to 2048). However,

due to the split architecture of the HI5735, the glitch is

moved to the 255 to 256 transition (and every subsequent

256 code transitions thereafter). This split R/2R segmented

current source architecture, which decreases the amount of

current switching at any one time, makes the glitch practi-

cally constant over the entire output range. By making the

glitch a constant size over the entire output range, this effec-

tively integrates this error out of the end application.

In measuring the output glitch of the HI5735 the output is

terminated into a 64Ω load. The glitch is measured at any

one of the current cell carry (code 255 to 256 transition or

any multiple thereof) throughout the DACs output range.

The glitch energy is calculated by measuring the area under

the voltage-time curve. Figure 13 shows the area considered

as glitch when changing the DAC output. Units are typically

specified in picoVolt-seconds (pV-s).

HI5735

(21) IOUT

100MHz SCOPE

LOW PASS

FILTER

64Ω

50Ω

FIGURE 12. GLITCH TEST CIRCUIT

1628

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