AD6654BBC datasheet(48/88 Pages) AD

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AD6654

Rev. 0 | Page 48 of 88

OUTPUT DATA ROUTER

The output data router circuit precedes the six AGCs of the

final output block and immediately follows interpolating half-

band filters. This block consists of two subblocks. The first

block is responsible for combining (interleaving) data from

more than one channel into a single stream of data. The second

block performs complex filter completion, as explained later in

this section. The combined data is passed on to the AGCs.

STREAM

CONTROL

PARALLEL

PORT A

PARALLEL

PORT C

PARALLEL

PORT B

AGC0

CH0

AGC1

CH1

AGC2

CH2

AGC3

CH3

AGC4

CH4

AGC5

CH5

Figure 55. Block Diagram of the Output Data Router

INTERLEAVING DATA

In some cases, filtering using a single channel is insufficient. For

such setups, it is advantageous to combine the filtering

resources of multiple channels rather than using filtering

resources from a single channel.

Multiple channels can be set up to co-process the ADC input

port data with the same NCO and filter setups. The decimation

phase values in one of the RCF filters are set such that the

channel’s filters are exactly out of phase with each other. In the

data router, these multiple channels are interleaved (combined)

to form a single stream of data. Because each individual channel

is decimated more than it would have been if a single channel

were filtering, more number-of-filter taps can be calculated.

This is best illustrated with an example:

Two channels need to work together to produce a filter at an

output rate of 9.216 MHz, when the input rate is 92.16 MHz.

Each channel is decimated by a factor of 20 (total decimation)

to achieve the desired output rate of 4.608 MHz each. This

compares to a decimation of 10, if a single channel were

working towards filtering.

The same coefficients are programmed into both of the

channels’ RCF filters, and the decimation phases are set to 0

and 1. The decimation phases can be set to 0 for one channel

and 1 for the second channel in the pair. This causes the first

channel to produce the even outputs of the filter, and the

second to produce the odd outputs of the filter. The streams

are then recombined (interleaved) to produce the desired

9.216 MHz output rate. The benefit is that now each channel’s

RCF has time to calculate twice as many taps, because it has a

lower output rate.

The interleaving function is a simple time-multiplexing func-

tion, with lower data rate on the input side and higher data rate

on the output side. The output data rate is the sum of all input

stream data rates that are combined.

The channels that need to be combined are programmable with

sufficient flexibility. Table 24 gives the combinations that are

possible using a 4-bit word (stream control bits) in the Parallel

Port Control 2 register.

Table 24. Stream Control Bit Combinations and Selections

Stream

Control Bits

Output Streams

Number of

Streams

0000

Ch 0, Ch 1 combined; Ch 2, Ch 3,

Ch 4, Ch 5 independent

0001

Ch 0, Ch 1, Ch 2 combined; Ch 3,

Ch 4, Ch 5 independent

0010

Ch 0, Ch 1, Ch 2, Ch 3 combined;

Ch 4, Ch 5 independent

0011

Ch 0, Ch 1, Ch 2, Ch 3, Ch 4

combined; Ch 5 independent

0100

Ch 0, Ch 1, Ch 2, Ch 3, Ch 4, Ch 5

combined

0101

Ch 0, Ch 1, Ch 2 combined; Ch 3,

Ch 4, Ch 5 combined

0110

Ch 0, Ch 1 combined; Ch 2, Ch 3

combined; Ch 4, Ch 5 combined

0111

Ch 0, Ch 1 combined; Ch 2, Ch 3

combined; Ch 4, Ch 5 independent

1000

Ch 0, Ch 1, Ch 2 combined; Ch 3,

Ch 4 combined; Ch 5 independent

1001

Ch 0, Ch 1, Ch 2, Ch 3 combined;

Ch 4, Ch 5 combined

Any other

state

Independent channels

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