データシートサーチシステム |
|
MC12181 データシート(PDF) 7 Page - Motorola, Inc |
|
MC12181 データシート(HTML) 7 Page - Motorola, Inc |
7 / 9 page MC12181 7 MOTOROLA RF/IF DEVICE DATA Figure 8. Closed Loop Frequency Response for ζ = 1 –60 –50 –40 –30 –20 –10 0 10 0.1 1.0 k Hz 1.0 10 100 3dB Bandwidth Natural Frequency To simplify analysis further a damping factor of 1 will be selected. The normalized closed loop response is illustrated in Figure 8 where the loop bandwidth is 2.5 times the loop natural frequency (the loop natural frequency is the frequency at which the loop would oscillate if it were unstable). Therefore the optimum loop bandwidth is 15 kHz/2.5 or 6.0 kHz (37.7 krads) with a damping coefficient, ζ ≈ 1. T(s) is the transfer function of the loop filter. T(s) + RoCos ) 1 NCo KpKv s2 ) RoCos ) 1 + 2 z wo s ) 1 1 wo2 s2 ) 2 z wo s ) 1 NCo KpKv + 1 wo2 ³ wo + KpKv NCo ³ Co + KpKv N wo2 RoCo + 2 z wo ³ z + woRoCo 2 ³ Ro + 2 z woCo where Nt = Total PLL Divide Ratio — 8×N where (N = 25...40) Kv = VCO Gain — Hz/V Kp = Phase Detector/Charge Pump Gain — A = ( |IOH| + |IOL| ) / 2 Technically, Kv and Kp should be expressed in Radian units [Kv (RAD/V), Kp (A/RAD)]. Since the component design equation contains the Kv × Kp term. the 2π cancels and the values can be epressed as above. Figure 9. Design Equations for the 2nd Order System In summary, follow the steps given below: Step 1: Plot the phase noise of crystal reference and the VCO on the same graph. Step 2: Increase the phase noise of the crystal reference by the noise contribution of the loop. Step 3: Convert the divide–by–N to dB (20log 8 × N) and increase the phase noise of the crystal reference by that amount. Step 4: The point at which the VCO phase noise crosses the amplified phase noise of the Crystal Reference is the point of the optimum loop bandwidth. This is approximately 15 kHz in Figure 7. Step 5: Correlate this loop bandwidth to the loop natural frequency per Figure 8. In this case the 3.0 dB bandwidth for a damping coefficient of 1 is 2.5 times the loop’s natural frequency. The relationship between the 3.0 dB loop bandwidth and the loop’s “natural” frequency will vary for different values of ζ. Making use of the equations defined in Figure 9, a math tool or spread sheet is useful to select the values for Ro and Co. Appendix: Derivation of Loop Filter Transfer Function The purpose of the loop filter is to convert the current from the phase detector to a tuning voltage for the VCO. The total transfer function is derived in two steps. Step 1 is to find the voltage generated by the impedance of the loop filter. Step 2 is to find the transfer function from the input of the loop filter to its output. The “voltage” times the “transfer function” is the overall transfer function of the loop filter. To use these equations in determining the overall transfer function of a PLL multiply the filter’s impedance by the gain constant of the phase detector then multiply that by the filter’s transfer function (Figure 10 contains the transfer function equations for 2nd, 3rd and 4th order PLL filters.) |
同様の部品番号 - MC12181 |
|
同様の説明 - MC12181 |
|
|
リンク URL |
プライバシーポリシー |
ALLDATASHEET.JP |
ALLDATASHEETはお客様のビジネスに役立ちますか? [ DONATE ] |
Alldatasheetは | 広告 | お問い合わせ | プライバシーポリシー | リンク交換 | メーカーリスト All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |