tipl - clocks and timing - pll building blocks part 1
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PLL Building Blocks Part 1 TI Precision Labs – Clocks and Timing Presented by Dean Banerjee Prepared by Liam Keese 1 Phase lock loop (PLL) block diagram 1/N N Divider 1/R Reference Oscillator R Divider KPD Phase Detector/ Charge Pump 1/D Z(s) Loop Filter VCO Output Divider 2 Voltage controlled oscillator (VCO) 1/N N Divider 1/R Reference Oscillator R Divider KPD Phase Detector/ Charge Pump 1/D Z(s) Loop Filter VCO Output Divider 3 VCO resonator L C 1 f 2 L C f = resonant frequency L = inductance C = capacitance L 2 g Tau = period L = length of the pendulum g = acceleration due to gravity 4 The real-world inductor R L XL 2 f L QL ( f ) RL R 5 Now add the stimulus R2 R1 Vcc L L C1 C1 C2 R3 RF Choke C2 Amplified signal from emitter is lightly coupled into the circuit to sustain oscillation 6 Example VCO circuit 7 VCO tuning range fMax Band ( O C co n V Overlap O 2) lV C and B ( CO co n V Tr a di tio Sili 3) na Sili frequency Switched Capacitor Bank Sili Overlap Band ( O C co n V 1) Overlap Sili and B ( CO co n V 0) fMin VMin Tuning voltage VMax 8 Phase lock loop overview 1/N N Divider fN fVCO fOSC 1/R Reference Oscillator R Divider fPD KPD Phase Detector/ Charge Pump 1/D Z(s) Loop Filter VCO fOUT Output Divider 9 High-frequency feedback (N) divider • N counter value – N = fVCO/fN = fVCO/fPD • Input to this counter can be high frequency • Prescalers are typically inside this counter 1/N fN N Divider KPD 1/R fPD Reference Oscillator R Divider Phase Detector/ Charge Pump 1/D Z(s) fVCO Loop Filter VCO Output Divider 10 High frequency feedback (N) divider Single Modulus Prescaler B Counter 1/P 1/N N Divider 1/R Reference Oscillator R Divider KPD Phase Detector/ Charge Pump 1/D Z(s) Loop Filter VCO Output Divider 11 High-frequency feedback (N) divider • Dual modulus prescaler • N = A x (P+1) + (B-A) x P = P x B+A A Counter Reference Oscillator R Divider Phase Detector/ Charge Pump 4/5 12 8/9 56 P/(P+1) P x (P-1) 1/(P+1) 1/N 1/R Minimum Continuous Divide 1/P B Counter KPD Prescaler 1/D Z(s) Loop Filter VCO Output Divider 12 Fractional dividers (Simple 1st order modulator) 1/900.2 N Divider KPD 1/10 1MHz 10 MHz Reference Oscillator R Divider Phase Detector/ Charge Pump 1/D Z(s) Loop Filter VCO 900.2 MHz Output Divider 13 Fractional dividers (Simple 1st order modulator) Fractional divide timing error 1/900.2 Phase Detector Cycle Accumul ator (Cycles) N Value 1 0.2 2 Time for Rising Edge for Dividers (ns) Actual Desired 900 999.7778 1000 0.4 900 1999.5557 2000 3 0.6 900 2999.3335 3000 4 0.8 900 3999.1113 4000 5 0 901 5000.0000 5000 N Divider 1/R Reference Oscillator R Divider KPD Phase Detector/ Charge Pump 1/D Z(s) Loop Filter VCO Output Divider 14 Fractional dividers (High-order modulators) Delta-Sigma Input S 1/N Fractional N Divider 1/R Reference Oscillator R Divider KPD Phase Detector/ Charge Pump Delta-Sigma Input 1 0,1 2nd 3rd 4th kth −1, 0, 1,2 −3, −2, −1, 0, 1, 2, 4 −7, ... , +8 −2k -1, ... , 2k 1/D Z(s) Loop Filter Delta-Sigma Order VCO Output Divider 15 Fractional dividers performance (fPD = 10 MHz) Spur and Fractional Noise Shaping Spur Example for fraction of 1/10 16 To find more clocks and timing technical resources and search products, visit ti.com/clocks 17 Short Quiz 1. True or False: The relationship between fVCO (VCO frequency), fPD (phase detector frequency), fn (N divider output frequency) is fVCO/fN = fVCO/fPD = N 18 Short Quiz 1. True or False: The relationship between fVCO (VCO frequency), fPD (phase detector frequency), fn (N divider output frequency) is fVCO/fN = fVCO/fPD = N 19 Short Quiz 2. Choose one: Which techniques can be used to increase VCO tuning range? (a) Fractional N divider (b) Switchable capacitor or inductor array (c) Output divider 20 Short Quiz 2. Choose one: Which techniques can be used to increase VCO tuning range (a) Fractional N divider (b) Switchable capacitor or inductor array (c) Output divider 21 Short Quiz 3. True or False: A fractional N modulator decreases the noise generated at higher frequencies. 22 Short Quiz 3. True or False: A fractional N modulator decreases the noise generated at higher frequencies 23 Short Quiz 4. Choose all that apply: Which of below statements apply when using a dual modulus prescaler? a) Counter will divide by (P+1) A times b) B < A c) N= P x B+A 24 Short Quiz 4. Choose all that apply: Which of below statements apply when using a dual modulus prescaler? a) Counter will divide by (P+1) A times b) B < A c) N= P x B+A 25 TI Information – Selective Disclosure