Low, High, Clock/Data Recovery, Reclocker

CYV15G0404RB

operates at, or near the rate of the incoming data stream for two primary cases:

•When the incoming data stream resumes after a time in which it was “missing.”

•When the incoming data stream is outside the acceptable signaling rate range.

To perform this function, periodically compare the frequency of the RXPLL VCO to the frequency of the TRGCLKx± input. If the VCO is running at a frequency beyond ±1500 ppm[21] as defined by the TRGCLKx± frequency, it is periodically forced to the correct frequency (as defined by TRGCLKx±, SPDSELx, and TRGRATEx) and then released in an attempt to lock to the input data stream.

Calculate the sampling and relock period of the Range Control as follows: RANGE_CONTROL_SAMPLING_PERIOD = (RECOVERED BYTE CLOCK PERIOD) * (4096).

During the time that the Range Control forces the RXPLL VCO to track TRGCLKx±, the LFIx output is asserted LOW. After a valid serial data stream is applied, it may take up to one RANGE CONTROL SAMPLING PERIOD before the PLL locks to the input data stream, after which LFIx is HIGH.

Table 2 lists the operating serial signaling rate and allowable range of TRGCLK± frequencies.

Table 2. Operating Speed Settings

		TRGCLKx±	Signaling
SPDSELx	TRGRATEx	Frequency	Signaling
SPDSELx	TRGRATEx	Frequency	Rate (Mbps)
		(MHz)	Rate (Mbps)
		(MHz)

LOW	1	Reserved	195–400
	0	19.5–40

MID (Open)	1	20–40	400–800

	0	40–80

HIGH	1	40–75	800–1500

	0	80–150

Receive Channel Enabled

The CYV15G0404RB contains four receive channels that it can independently enable and disable. Each channel are enabled or disabled separately through the RXPLLPDx input latch as controlled by the device configuration interface. RXPLLPDx latch = 0 disables the associated PLL and analog circuitry of the channel. Any disabled channel indicates a constant link fault condition on the LFIx output. RXPLLPDx = 1 enables the associated PLL and receive channel to receive a serial stream.

Note When a disabled receive channel is reenabled, the status of the associated LFIx output and data on the parallel outputs for the associated channel may be indeterminate for up to 2 ms.

Clock/Data Recovery

A separate CDR block within each receive channel performs the extraction of a bit rate clock and recovery of bits from each received serial stream. An integrated PLL that tracks the frequency of the transitions in the incoming bit stream and aligns the phase of the internal bit rate clock to the transitions

Document #: 38-02102 Rev. *C

in the selected serial data stream performs the clock extraction function.

Each CDR accepts a character-rate (bit-rate ÷ 10) or half-character-rate (bit-rate ÷ 20) training clock from the associated TRGCLKx± input. This TRGCLKx± input is used to

•Ensure that the VCO (within the CDR) is operating at the correct frequency (rather than a harmonic of the bit rate)

•Reduce PLL acquisition time

•Limit unlocked frequency excursions of the CDR VCO when there is no input data present at the selected Serial Line Receiver.

Regardless of the type of signal present, the CDR attempts to recover a data stream from it. If the signaling rate of the recovered data stream is outside the limits set by the range control monitors, the CDR tracks TRGCLKx± instead of the data stream. Once the CDR output (RXCLK±) frequency returns close to TRGCLKx± frequency, the CDR input switches back to the input data stream. If no data is present at the selected line receiver, this switching behavior may cause brief RXCLK± frequency excursions from TRGCLKx±. However, the LFIx output indicates the validity of the input data stream. The frequency of TRGCLKx± must be within ±1500 ppm[21] of the frequency of the clock that drives the reference clock input of the remote transmitter, to ensure a lock to the incoming data stream. This large ppm tolerance allows the CDR PLL to reliably receive a 1.485 or 1.485/1.001 Gbps SMPTE HD-SDI data stream with a constant TRGCLK frequency.

For systems using multiple or redundant connections, use the LFIx output to select an alternate data stream. When the device detects an LFIx indication, external logic toggles selection of the associated INx1± and INx2± input through the associated INSELx input. When a port switch takes place, the receive PLL for that channel reacquires the new serial stream.

Reclocker

Each receive channel performs a reclocker function on the incoming serial data. To do this, the Clock and Data Recovery PLL first recovers the clock from the data. The recovered clock retimes the data and then passes it to an output register. It also passes the recovered character clock from the receive PLL to the reclocker output PLL, which generates the bit clock that clocks the retimed data into the output register. This data stream is then transmitted through the differential serial outputs.

Reclocker Serial Output Drivers

The serial output interface drivers use differential Current Mode Logic (CML) drivers to provide source-matched drivers for 50Ω transmission lines. These drivers accept data from the reclocker output register in the reclocker channel. These drivers have signal swings equivalent to that of standard PECL drivers, and can drive AC coupled optical modules or trans- mission lines.

Reclocker Output Channels Enabled

Each driver can be enabled or disabled separately via the device configuration interface.

When a driver is disabled using the configuration interface, it internally powers down to reduce device power. If both

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