3D7522 Datasheet, PDF (2/4 Pages) Data Delay Devices, Inc. – MONOLITHIC MANCHESTER DECODER

3D7522
APPLICATION NOTES
The 3D7522 Manchester Decoder samples the
input at precise pre-selected intervals to retrieve
the data and to recover the clock from the
received data stream. Its architecture comprises
finely tuned delay elements and proprietary
circuitry which, in conjunction with other circuits,
implement the data decoding and clock recovery
function.
INPUT SIGNAL CHARACTERISTICS
Encoded data transmitted from a source arrives
at its destination corrupted. Such corruption of
the received data manifests itself as jitter and/or
pulse width distortion at the input to the device.
The instantaneous deviations from nominal Baud
Rate and/or Pulse Width (high or low) adversely
impact the data extraction and clock recovery
function if their published limits are exceeded.
See Table 4, Allowed Baud Rate/Duty Cycle.
The 3D7522 Manchester Decoder Data Input is
TTL compatible. The user should assure that
the 1.5 volt TTL threshold is used when referring
to all timing, especially the input pulse widths.
FREQUENCY (JITTER) ERRORS
The 3D7522 Manchester Decoder, being a self-
timed device, is tolerant of frequency modulation
(jitter) present in the input data stream, provided
that the input data pulse width variations remain
within the allowable ranges.
OUTPUT SIGNAL CHARACTERISTICS
The 3D7522 presents at its outputs the decoded
data (inverted) and the recovered clock. The
decoded data is valid at the rising edge of the
clock.
The clock recovery function operates in two
modes dictated by the input data stream bit
sequence. When a data bit is succeeded by its
inverse, the clock recovery circuit is engaged and
forces the clock output low for a time equal to
one over twice the baud rate. Otherwise, the
input is presented at the clock output unchanged,
shifted in time.
When engaged, the clock recovery circuit
generates a low-going pulse of fixed width.
Therefore, the clock duty cycle is strongly
dependent on the baud rate, as this will affect
the clock-high duration.
The clock output falling edge is not operated on
by the clock recovery circuitry. It, therefore,
preserves more accurately the clock frequency
information embedded in the transmitted data.
Therefore, it can be used, if it is desired, to
retrieve clock frequency information.
POWER SUPPLY AND
TEMPERATURE CONSIDERATIONS
CMOS integrated circuitry is strongly dependent
on power supply and temperature. The
monolithic 3D7522 Manchester Decoder utilizes
novel and innovative compensation circuitry to
minimize timing variations induced by fluctuations
in power supply and/or temperature.
.
ENCODED
0
1
0
1
1
0
0
1
RECEIVED
(RX)
CLOCK
(CLK)
DATA
(DATB)
DECODED
t_C
t_CL
t_{CW L}
t_CD
1
0
1
1
0
0
1
Figure 1: Timing Diagram
Doc #06002
DATA DELAY DEVICES, INC.
2
10/31/2007
Tel: [phone] Fax: [phone] http://www.datadelay.com