DS125DF111: PRBS Generator

Sean Iwasaki

Intellectual 400 points

Part Number: DS125DF111
Other Parts Discussed in Thread: DS110DF111

Dear TI Support:

Can the PRBS generator free run at the last known VCO frequency lock with input signal and without input signal?

Would the PRBS generator tolerance relate to the oscillator tolerance?

over 5 years ago

0 Rodrigo Natal over 5 years ago

TI__Mastermind 19235 points

Hi,

The DS125DF111 can be configured as PRBS generator when there is a valid input signal that the CDR can lock to.

Table. PRBS Generator Programming Sequence: Requires Valid and Locked Input Data Pattern

STEP	REGISTER ADDRESS	REGISTER DATA	REGISTER MASK	COMMENTS
1	0xFF	0x0C	0xFF (write bits[7:0])	Enable Broadcast
2	0x09	0x20	0x20 (only write bit[5])	Override Loopthru Select
3	0x1E	0x80	0xE0 (only write bits[7:5])	Output MUX Select PRBS Generator
4	0x1E	0x10	0x10	Power-up PRBS Generator
5	0x30	0x08	0x08	Power-up PRBS Clock
6	0x30	0x00	0x03	Select PRBS9 pattern (511 bits)
7	0x0D	0x20	0x20	Enable PRBS Clock

Notes:

1. To select PRBS31 instead of PRBS9, change Register Data 0x30 = 0x02 with mask of 0x03 in Step 6.

2. To only select Channel A, change Register Data 0xFF = 0x04 in Step 1.

3. To only select Channel B, change Register Data 0xFF = 0x05 in Step 1.

4. It has been noted in product testing that some pattern analyzers use an alternate PRBS9 polarity.

It is also feasible to configure this retimer to PRBS generator while operating in free VCO running mode with no input signal present. For this free VCO run PRBS generation mode we can target a VCO frequency via the selection of the cap count value (via channel register 0x08) but we cannot guarantee an exact frequency or PPM tolerance. Refer to the channel register write routine below for enabling VCO free run PRBS generator with VCO frequency ~ 10.3G

Enable the VCO free run generator

For DS110DF111, the settings below will produce a VCO free run frequency around 10.3G. As the resulting frequency will vary across process voltage and temp, the user may need to adjust reg_0x08 to tune the VCO frequency.

Table. Programming Sequence: PRBS Generator with Free-Running VCO @ ~10.3 Gbps, No Input Data Required

STEP	REGISTER ADDRESS	REGISTER DATA	REGISTER MASK	COMMENTS
1	0xFF	0x0C	0xFF (write bits[7:0])	Enable Broadcast
2	0x00	0x04	0x04 (only write bit[2])	Reset Channel Registers
3	0x14	0x80	0x80 (only write bit[7])	Preset Signal Detect
4	0x09	0x04	0x04	Override divider select
5	0x09	0x80	0x80	Override VCO cap count
6	0x08	0x06	0x1F	Set VCO cap count to 06'h
7	0x18	0x00	0x70	Select divider select to 000'b
8	0x09	0x08	0x08	Override charge pump power downs
9	0x1B	0x00	0x03	Disable both charge pumps
10	0x09	0x40	0x40	Override Loop-filter DAC
11	0x1F	0x12	0x1F	Set Loop-filter DAC override value
12	0x1E	0x10	0x10	Enable PRBS Generator
13	0x30	0x08	0x0F	Enable Digital Clock - set pattern to PRBS9
14	0x09	0x20	0x20	Override Loopthru Select
15	0x1E	0x80	0xE0	Output MUX Select PRBS Generator
16	0x0D	0x20	0x20	PRBS Seed Load

Notes:

1. To select PRBS31 instead of PRBS9, change Register Data 0x30 = 0x0A in Step 13.

2. To achieve a higher data-rate in Step 6 decrease VCO cap count value.

3. To achieve a lower data-rate in Step 6 increase the VCO cap count value.

4. To only select Channel A, change Register Data 0xFF = 0x04 in Step 1.

5. To only select Channel B, change Register Data 0xFF = 0x05 in Step 1.

6. With a free running VCO the actual output frequency will change with temperature and voltage. BERT is not recommended in this mode.

Regards,

Rodrigo Natal

HSSC Applications Engineer

0 Sean Iwasaki over 5 years ago in reply to Rodrigo Natal

Intellectual 400 points

Rodrigo:

Thank you very much for your reply and information. I greatly appreciate your help.

Sincerely

Sean

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DS125DF111: PRBS Generator