What are the various Electrical parameters required for the Type-C to DisplayPort cable design?
Following aspects need to be taken care while designing a Type-C to DP cable:
- Insertion loss and Return loss must be tested relative to an 85Ω differential environment at the USB Type-C connector and relative to a 100Ω differential environment at the DisplayPort connector. Note that with respect to USB Type-C, fmax = 12.15 GHz and Tb = 123.4 ps.
- The intra-pair skew should be limited to 30 ps to support 2m cables at 15 ps/m.
- The Insertion Loss Fit at Nyquist Frequency (ILFitAtNq) should meet the following requirements:
- ≥ -5.5 dB at 1.35 GHz (High Bit Rate (HBR))
- ≥ -8.5 dB at 2.7 GHz (High Bit Rate 2 (HBR2))
- ≥ -11.0 dB at 4.05 GHz (High Bit Rate 3 (HBR3))
1.35, 2.7, and 4.05 GHz are the Nyquist frequencies for HBR, HBR2 and HBR3 respectively.
- For the Input Pulse Spectrum (used in the calculation of integrated multi-reflection (IMR)), the DisplayPort HBR, HBR2 and HBR3 correspond to a Unit Interval (UI) of 370.4, 185.2 and 123.5 ps respectively. The rise time is 0.4UI. IMR has dependency on ILFitAtNq. More IMR may be tolerated when ILFitAtNq decreases. The IMR limit is specified as a function of ILFitAtNq: IMR ≤ 0.0579 * ILFitAtNq2 + 1.64 * ILFitAtNq - 30.23
- The power sum limits for integrated crosstalk between the DisplayPort lanes must comply with the following limits:
- IFEXT ≤ -35 dB (up to 12 GHz)
- INEXT ≤ -35 dB (up to 12 GHz) when measured through the USB Type-C connector
- INEXT ≤ -33 dB (up to 12 GHz) when measured through the DisplayPort connector
- Integrated Return Loss (IRL) has a strong dependency on ILFitAtNq, and its limit is specified as a function of ILFitAtNq: IRL ≤ 0.0336 * ILFitAtNq2 + 1.28 * ILFitAtNq - 10.87
- Differential to Common mode conversion (SCD12/SCD21) shall be ≤ -17 dB from 100 MHz to 8.1 GHz.