Referenceless clock recovery circuit with wide frequency acquisition range
View Patent ↗A full-rate referenceless clock-data recovery architecture with neither a frequency detector nor a lock detector that allows both frequency and phase locking in a single loop. According to one embodiment, a referenceless clock data recovery (CDR) circuit, comprises a digital control circuit (DCC), a phase and strobe point detector circuit (PSPD), and an LC voltage control oscillator (LC VCO) electrically coupled to the PSPD and DCC such that a frequency of the LC VCO decreases when a negative strobe point is detected and an initial frequency of the LC VCO is higher than an input data bit rate.
1. A referenceless clock data recovery (CDR) circuit, comprising:
a digital control circuit (DCC) configured to generate a strobe point voltage (Vsp);
a phase and strobe point detector circuit (PSPD) electrically coupled to the DCC and configured to detect the strobe point voltage (Vsp) generated by the DCC and set a strobe point (SP) according to the strobe point voltage (V sp ); and
an LC voltage control oscillator (LC VCO) electrically coupled to the PSPD and DCC, wherein the LC VCO is configured to detect the strobe point (SP) set by the PSPD and to decrease a frequency of the LC VCO when the strobe point (SP) is negative and an initial frequency of the LC VCO is higher than an input data bit rate.
2. The CDR circuit of claim 1 , wherein the PSPD comprises a Hogge phase detector (PD).
3. The CDR of claim 2 , wherein the PSPD further comprises a tunable buffer.
4. The CDR of claim 3 , wherein the tunable buffer comprises triode-based PMOS transistors.
5. The CDR of claim 1 , further comprising a capacitor bank.
6. The CDR of claim 5 , wherein the capacitor bank has a resolution of 5 bits.
7. A method of frequency locking a clock data recovery (CDR) circuit, comprising:
generating a strobe point voltage (V SP ) by a digital control circuit (DCC);
detecting the strobe point voltage (V SP ) by a phase and strobe point detector circuit (PSPD) and setting a strobe point (SP) according to the strobe point voltage (Vs sp ); and
phase and frequency locking the CDR circuit once a voltage control oscillator (VCO) has reached a desired frequency based on the polarity of the SP and an input data bit rate.
8. The method of claim 7 , further comprising adjusting the SP by changing a difference between delays of a first tunable buffer and a second tunable buffer.
9. The method of claim 7 , wherein frequency locking comprises adjusting, by the PSPD, the VCO frequency.
10. The method of claim 7 , further comprising setting the SP to be very close to zero once the CDR circuit is locked.
11. The method of claim 7 , further comprising using a frequency acquisition algorithm to set the polarity of the SP.
12. The method of claim 11 , further comprising using the frequency acquisition algorithm to search a correct band in a capacitor bank while in the CDR is in frequency acquisition mode (FAM).
13. The method of claim 7 , further comprising converting a voltage output from the PSPD to a current I SPD ; and integrating the current I SPD onto a capacitor of the DCC to bring the SP close to zero in a phase adjustment mode (PAM).