AD8116JSTZ Datasheet AD8116JSTZ | P13-P15

AD8116

–12–

Using additional crosspoint devices in the design can lower the

number of outputs that have to be wire-ORed together. Figure

shows a block diagram of a system using ten AD8116s tocreate a

nonblocking 128 × 16 crosspoint that restricts the wire-ORing at

the output to only four outputs. This will prevent anenabled

output from having to drive a large number of disableddevices.

Additionally, by using the lower eight outputs fromeach of the

two Rank 2 AD8116s, a blocking 128 × 32 crosspointarray can be

realized.

There are, however, some drawbacks to this technique. The

offset voltages of the various cascaded devices will accumulate

and the bandwidth limitations of the devices will compound. In

addition, the extra devices will consume more current and take

up more board space. Once again, the overall system design

specifications will determine how to make the various trade-offs.

OUT

AD8116

OUT

AD8116

0–15

AD8116

OUT

AD8116

16–31

OUT 16–31

0–15

16–31

OUT 0–15

OUT

Figure 6. 32

32 Crosspoint Array Using Four AD8116s

OUT

AD8116

IN OUT

AD8116

0–15

OUT

AD8116

16–31

AD8116

32–47

16 16 16

OUT 0–15

OUT 16–31

OUT 32–47

OUT

OUT OUT

OUT

OUT OUT

Figure 7. 48

48 Crosspoint Array Using Nine AD8116s

Creating Larger Crosspoint Arrays

The AD8116 is a high density building block for crosspoint

arrays over 256 × 256. Various features such as output disable,

chip enable, serial data out and multiple pinouts for logic signals

are very useful for the creation of these larger arrays.

The first consideration in constructing a larger crosspoint is to

determine the minimum number of devices that are required.

The 16 × 16 architecture of the AD8116 contains 256 “points,”

which is a factor of four greater than an 8 × 8 crosspoint and a

factor of 64 greater than a 4 × 1 crosspoint. The PC board area

and power consumption savings are readily apparent when

compared to using these smaller devices.

For a nonblocking crosspoint, the number of points required is

the product of the number of inputs multiplied by the number

of outputs. Nonblocking requires that the programming of a

given input to one or more outputs does not restrict the avail-

ability of that input to be a source for any other outputs.

Thus a 32 × 32 crosspoint will require 1024 points. This number is

then divided by 256, or the number of points in one AD8116

device, to yield four in this case. This says that the minimum

number of 16 × 16 devices required for a fully programmable

32 × 32 crosspoint is four.

Some nonblocking crosspoint architectures will require more

than this minimum as calculated above. Also, there are blocking

architectures that can be constructed with fewer devices than this

minimum. These systems have connectivity available on a statis-

tical basis that is determined when designing the overall system.

The basic concept in constructing larger crosspoint arrays is to

connect inputs in parallel in a horizontal direction and to “wire-

OR” the outputs together in the vertical direction. The meaning

of horizontal and vertical can best be understood by looking at a

diagram. Figure 6 illustrates this concept for a 32 × 32 crosspoint

array. A 48 × 48 crosspoint is illustrated in Figure 7.

The 32 × 32 crosspoint requires each input driver drive two inputs

in parallel and each output be wire-ORed with one other output.

The 48 × 48 crosspoint requires driving three inputs in parallel and

having the outputs wire-ORed in groups of three. It is required of

the system programming that only one output of a wired-OR node

be active at a time.

It is not essential that crosspoint architectures be square. For

example, a 64 × 16 crosspoint array can be constructed with

four AD8116s by driving each input with a separate signal

and wire-ORing together the corresponding outputs of each

device. It can be seen, however, that by going to larger arrays

the number of disabled outputs an active output has to drive

starts to increase.

At some point, the number of outputs that are wire-ORed becomes

too great to maintain system performance. This will vary according

to which system specifications are most important. For example, a

128 × 16 crosspoint can be created with eight AD8116s. This

design will have 128 separate inputs and have the corresponding

outputs of each device wire-ORed together in groups of eight.

REV. C

AD8116

–13–

IN 16–31

IN 0–15

OUT 0–16

IN 32–47

IN 48–63

IN 64–79

IN 80–95

IN 96–111

IN 112–127

NONBLOCKING

OUTPUTS

ADDITIONAL

16 OUTPUTS

RANK 2

32:16 NONBLOCKING

(32:32 BLOCKING)

RANK 1

(128:32)

FOUR AD8116 OUTPUTS

WIRE-ORED TOGETHER

Figure 8. Nonblocking 128

16 Array (128

32 Blocking)

Logic Operation

There are two basic options for controlling the logic in multi-

crosspoint arrays. One is to serially connect the data paths

(DATA OUT to DATA IN) of all the devices and tie all the

CLK and UPDATE signals in parallel. CE can be tied low for all

the devices. A long serial sequence with the desired programming

data consisting of 80 bits times the number of AD8116 devices can

then be shifted through all the parallel devices by using the DATA

IN of the first device and the CLK. When finished clocking

in the data, UPDATE can be pulled low to program all the

device crosspoint matrices.

This technique has an advantage in that a separate CE signal is not

required for each chip, but has a disadvantage in that several chips’

data cannot be shifted in parallel. In addition, if another device is

added into the system between already existing devices, the pro-

gramming sequence will have to be lengthened at some midpoint

to allow for programming of the added device.

The second programming method is to connect all the CLK and

the DATA IN pins in parallel and use the CE pins in sequence to

program each device. If a byte or 16-bit word of data is available

for providing the programming data, then multiple AD8116s can

be programmed in parallel with just 80 clock cycles. This method

can be used to speed up the programming of large arrays. Of

course, in a practical system, various combinations of these

basic methods can be used.

Power-On Reset

Most systems will want all the AD8116s to be in the reset state

(all outputs disabled) when power is applied to the system. This

ensures that two outputs that are wire-ORed together will not

fight each other at power up.

The power-on reset function can be implemented by adding a

0.1 μF capacitor from the RESET pin to ground. This will hold

this signal low after the power is applied to reset the device. An

on-chip 20 kΩ resistor from RESET to DVCC will charge the

capacitor to the logical high state. If several AD8116s are used,

the pull-up resistors will be in parallel, so a larger value capaci-

tance should be used.

If the system requires the ability to be reset while power is still

applied, the RESET driver will have to be able to charge and

discharge this capacitance in the required time. With too many

devices in parallel, this might become more difficult; if this

occurs, the reset circuits should be broken up into smaller sub-

sets with each controlled by a separate driver.

CROSSTALK

Many systems, such as broadcast video, that handle numerous

analog signal channels have strict requirements for keeping the

various signals from influencing any of the others in the system.

Crosstalk is the term used to describe the coupling of the signals

of other nearby channels to a given channel.

When there are many signals in close proximity in a system, as

will undoubtedly be the case in a system that uses the AD8116,

the crosstalk issues can be quite complex. A good understanding

of the nature of crosstalk and some definition of terms is required

in order to specify a system that uses one or more AD8116s.

Types of Crosstalk

Crosstalk can be propagated by means of any of three methods.

These fall into the categories of electric field, magnetic field

and sharing of common impedances. This section will explain

these effects.

Every conductor can be both a radiator of electric fields and a

receiver of electric fields. The electric field crosstalk mecha-

nism occurs when the electric field created by the transmitter

propagates across a stray capacitance and couples with the

receiver and induces a voltage. This voltage is an unwanted

crosstalk signal in any channel that receives it.

Currents flowing in conductors create magnetic fields that

circulate around the currents. These magnetic fields will then

generate voltages in any other conductors whose paths they

link. The undesired induced voltages in these other channels

are crosstalk signals. The channels that crosstalk can be said

to have a mutual inductance that couples signals from one

channel to another.

The power supplies, grounds and other signal return paths of a

multichannel system are generally shared by the various channels.

When a current from one channel flows in one of these paths, a

voltage that is developed across the impedance becomes an

input crosstalk signal for other channels that share the common

impedance.

All these sources of crosstalk are vector quantities, so the

magnitudes cannot be simply added together to obtain the total

crosstalk. In fact, there are conditions where driving additional

circuits in parallel in a given configuration can actually reduce

the crosstalk.

Areas of Crosstalk

For a practical AD8116 circuit, it is required that it be mounted

to some sort of circuit board in order to connect it to power

supplies and measurement equipment. Great care has been

taken to create a characterization board that adds minimum

crosstalk to the intrinsicdevice. This, however, raises the issue

that a system’s crosstalkis a combination of the intrinsic

crosstalk of the devices and theDJSDVJUCPBSEUPXIJDIUIFZBSF

REV. C

AD8116

–14–

mounted. It is important to tryto separate these two areas of

crosstalk when attempting tominimize its effect.

In addition, crosstalk can occur among the input circuits to a

crosspoint and among the output circuits. Techniques will be

discussed for diagnosing which part of a system is contributing

to crosstalk.

Measuring Crosstalk

Crosstalk is measured by applying a signal to one or more channels

and measuring the relative strength of that signal on a desired

selected channel. The measurement is usually expressed as dB

down from the magnitude of the test signal. The crosstalk is

expressed by:

|XT| = 20 log

(Asel(s)/Atest(s))

where s = jω is the Laplace transform variable, Asel(s) is the

amplitude of the crosstalk-induced signal in the selected chan-

nel and Atest(s) is the amplitude of the test signal. It can be

seen that crosstalk is a function of frequency, but not a function

of the magnitude of the test signal. In addition, the crosstalk

signal will have a phase relative to the test signal associated

with it.

A network analyzer is most commonly used to measure crosstalk

over a frequency range of interest. It can provide both magnitude

and phase information about the crosstalk signal.

As a crosspoint system or device grows larger, the number

of theoretical crosstalk combinations and permutations can

become extremely large. For example, in the case of the 16 × 16

matrix of the AD8116, we can examine the number of crosstalk

terms that can be considered for a single channel, say IN00 input.

IN00 is programmed to connect to one of the AD8116 outputs

where the measurement can be made.

First, we can measure the crosstalk terms associated with driv-

ing a test signal into each of the other 15 inputs one at a time.

We can then measure the crosstalk terms associated with driving a

parallel test signal into all 15 other inputs taken two at a time in all

possible combinations; and then three at a time, etc., until, finally,

there is only one way to drive a test signal into all 15 other inputs.

Each of these cases is legitimately different from the others and

might yield a unique value depending on the resolution of the

measurement system, but it is hardly practical to measure all these

terms and then to specify them. In addition, this describes the

crosstalk matrix for just one input channel. A similar crosstalk

matrix can be proposed for every other input. In addition, if the

possible combinations and permutations for connecting inputs to

the other (not used for measurement) outputs are taken into

consideration, the numbers rather quickly grow to astronomical

proportions. If a larger crosspoint array of multiple AD8116s is

constructed, the numbers grow larger still.

Obviously, some subset of all these cases must be selected to be

used as a guide for a practical measure of crosstalk. One common

term is “all hostile” crosstalk. This term means that all other sys-

tem channels are driven in parallel, and the crosstalk to the selected

channel is measured. In general, this will yield the worst crosstalk

number, but this is not always the case.

Other useful crosstalk measurements are those created by one

nearest neighbor or by the two nearest neighbors on either side. These

crosstalk measurements will generally be higher than those of more

distant channels, so they can serve as a worst case measure for any

other one-channel or two-channel crosstalk measurements.

Input and Output Crosstalk

The flexible programming capability of the AD8116 can be

used to diagnose whether crosstalk is occurring more on the

input side or the output side. Some examples are illustrative.

A given input channel (IN07 in the middle for this example)

can be programmed to drive OUT07. The input to IN07 is

just terminated to ground and no signal is applied.

All the other inputs are driven in parallel with the same test

signal (practically provided by a distribution amplifier), but

all other outputs except OUT07 are disabled. Since grounded

IN07 is programmed to drive OUT07, there should be no

signal present. Any signal that is present can be attributed to

the other 15 hostile input signals, because no other outputs

are driven. Thus, this method measures the all-hostile input

contribution to crosstalk into IN07. Of course, the method

can be used for other input channels and combinations of

hostile inputs.

For output crosstalk measurement, a single input channel is

driven (IN00 for example) and all outputs other than a given

output (IN07 in the middle) are programmed to connect to

IN00. OUT07 is programmed to connect to IN15 which is

terminated to ground. Thus OUT07 should not have a signal

present since it is listening to a quiet input. Any signal mea-

sured at the OUT07 can be attributed to the output crosstalk

of the other 15 hostile outputs. Again, this method can be

modified to measure other channels and other crosspoint

matrix combinations.

Effect of Impedances on Crosstalk

The input side crosstalk can be influenced by the output imped-

ance of the sources that drive the inputs. The lower the impedance

of the drive source, the lower the magnitude of the crosstalk. The

dominant crosstalk mechanism on the input side is capacitive

coupling. The high impedance inputs do not have significant cur-

rent flow to create magnetically induced crosstalk.

From a circuit standpoint, the input crosstalk mechanism looks

like a capacitor coupling to a resistive load. For low frequencies

the magnitude of the crosstalk will be given by:

|XT| = 20 log

[(R

) × s]

where R

is the source resistance, C

is the mutual capacitance

between the test signal circuit and the selected circuit, and s is

the Laplace transform variable.

From the equation it can be observed that this crosstalk mecha-

nism has a high pass nature; it can be also minimized by reducing

the coupling capacitance of the input circuits and lowering

the output impedance of the drivers. If the input is driven from

a 75 Ω terminated cable, the input crosstalk can be reduced by

buffering this signal with a low output impedance buffer.

On the output side, the crosstalk can be reduced by driving a

lighter load. Although the AD8116 is specified with excellent

differential gain and phase when driving a standard 150 Ω video

load, the crosstalk will be higher than the minimum due to the

high output currents. These currents will induce crosstalk via

the mutual inductance of the output pins and bond wires of the

AD8116.

REV. C

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P17

AD8116JSTZ

Mfr. #:

Buy AD8116JSTZ

Manufacturer:

Analog Devices Inc.

Description:

Analog & Digital Crosspoint ICs 200MHz 16 x 16 Buffered

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

Products related to this Datasheet

AD8116JSTZ