AD650KP Ver la hoja de datos (PDF) - Analog Devices

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componentes Descripción

Fabricante

AD650KP

Voltage-to-Frequency and Frequency-to-Voltage Converter

Analog Devices 

AD650

jumper cable. The signal at this point is a 5 volt digital pulse train

and as such may be transmitted in any fashion suitable to the appli-

cation at hand. For example, galvanic isolation is achieved with a

simple transformer or opto-isolator; extremely high voltage isola-

tion or transmission through severe RF environments can be ac-

complished with a fiber-optic link; telemetry can be accomplished

with a radio link. The actual method of conveying the pulses is not

crucial to the system performance. The PLL is the circuit shown in

Figure 14, and the filter shown on the output signal is simply to at-

tenuate carrier feedthrough to allow easy interpretation of the sig-

nal with an oscilloscope and spectrum analyzer.

The step response of the system is shown in Figure 16a. The

signal output is swinging between 5 volts and 10 volts, for an

input step of 500 kHz to 1 MHz. Note that the AD650 is actu-

ally overshooting to 1.1 MHz and the response remains well

controlled. Note the slight irregularity during the transition: this

is caused by cycle slipping during the slew where feedback is lost

temporarily and the PLL actually loses phase lock. The fre-

quency response of the system when driven with sine wave exci-

tation is shown in Figure 16b. Here the output level is set to

2 volts peak-to-peak, and the carrier is 800 kHz. Note that the

–3 dB bandwidth is about 70 kHz, which is consistent with a

damping factor of 0.8 and a natural frequency of 35 kHz.4 When

an unmodulated carrier is applied to the PLL, the noise that ap-

pears at the output determines the dynamic range of the system.

The spectrum of the noise at the output of the PLL is shown in

Figure 16c. By comparing this with Figure 16b, the dynamic

range of the system is seen to be 80 dB. The harmonic distortion

of the system is shown in Figure 16d. The output is a 2 V p-p

sine wave at 5 kHz, and the amplitude of the first harmonic is

seen to be 48 dB below the fundamental. The harmonic distortion

can be improved to the level of 60 dB by reducing the ampli-

tude of the modulation, but this is at the expense of dynamic

range since the intensity of the noise floor remains constant.

Figure 16c. Noise Output from PLL

Figure 16d. Harmonic Distortion of PLL System

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

"D" Package (TO-116)

Ceramic DIP

"N" Package

Plastic DIP

Figure 16a. Step Response

"P" Package

PLCC

Figure 16b. Frequency Response

4See page 13 of reference 3.

–12–

REV. A

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