AD8129ARM datasheet(22/28 Pages) AD

22 / 28 page

REV. 0

AD8129/AD8130

–22–

–10

–20

–30

–40

–50

–60

–70

–80

FREQUENCY – Hz

10k

100k

10M

100M

Figure 8. Transmission Response of 300 m of

Category 5 Cable

The feedback network is between Pins 6 and 5 and from Pin 5

to ground. C1 and RF create a corner frequency of about 800 kHz.

The gain increases to provide about 15 dB of boost at 8 MHz.

The response of this circuit is shown in Figure 9.

–10

–20

–30

–40

–50

–60

–70

–80

FREQUENCY – Hz

10k

100k

10M

100M

Figure 9. Frequency Response of Equalizer Circuit

It is difficult to come up with the exact component values via

strictly mathematical means, because the equations for the cable

attenuation are approximate and have functions that are not

simply related to the responses of RC networks. The method

used in this design was to approximate the required response via

graphical means from the frequency response, and then select

components that would approximate this response. The circuit

was then built and measured, and finally adjusted to obtain an

acceptable response—in this case flat to 9 MHz to within

approximately 1 dB. (See Figure 10.)

–10

–20

–30

–40

–50

–60

–70

–80

FREQUENCY – Hz

10k

100k

10M

100M

Figure 10. Combined Response of Cable Plus Equalizer

Output Offset/Level Translator

The circuit in Figure 6 has the reference input (Pin 4) tied to

ground, which produces a ground-referenced output signal. If it is

desired to offset the output voltage from ground, the REF input

can be used. (See Figure 11). The level VOFFSET appears at the

output with unity gain.

0.1 F10 F

–V

VOUT = VIN +VOFFSET

0.1 F

10 F

VIN

VOFFSET

–VS

+VS

AD8130

Figure 11. The voltage applied to Pin 4 adds to the unity-

gain output voltage produced by VIN.

If the circuit has a gain higher than unity, the gain has to be

factored in. If RG is connected to ground, the voltage applied to

REF will be multiplied by the gain of the circuit and appear at

the output; just like a noninverting conventional op amp, This

situation is not always desirable and one may want VOFFSET to

appear at the output with unity gain.

One way to accomplish this is to drive both REF and RG with

the desired offset signal. (See Figure 12.) Superposition can be

used to solve this circuit. First break the connection between

VOFFSET and RG. With RG grounded the gain from Pin 4 to

VOUT will be 1 + RF/RG. With Pin 4 grounded, the gain though

RG to VOUT is –RF/RG. The sum of these is +1. If VREF is delivered

from a low-impedance source, this will work fine. However, if

the delivered offset voltage is derived from a high-impedance

source, like a voltage divider, its impedance will affect the gain

equation. This makes the circuit more complicated as it creates

an interaction between the gain and offset voltage.

AD8129ARM датащи(PDF) 22 Page - Analog Devices

AD8129ARM датащи(HTML) 22 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

датащи скачать

ссылки URL