поискавой системы для электроныых деталей |
|
GS1515-CQM датащи(PDF) 9 Page - Gennum Corporation |
|
GS1515-CQM датащи(HTML) 9 Page - Gennum Corporation |
9 / 17 page 522 - 23 - 01 9 During pathological signals, the amount of jitter that the phase detector will add can be calculated. By choosing the proper loop bandwidth, the amount of phase detector induced jitter can also be limited. Typically, for a 1.41MHz loop bandwidth at 0.2UI input jitter modulation, the phase detector induced jitter is about 0.015UIp-p. This is not very significant, even for the pathological signals. CHARGE PUMP The charge pump in a slew PLL is different from the charge pump in a linear PLL. There are two main functions of the charge pump. One function is to hold the frequency information of the input data. This information is held by CCP1, which is connected between LFS and LFS. The other capacitor, CCP2 between LFS and LFA_GND is used to remove common mode noise. Both CCP1, CCP2 should be the same value. The second function of the charge pump is to provide a binary control voltage to the VCO depending upon the phase detector output. The output pin, LFA controls the VCO. Internally there is a 500 Ω pull-up resistor, which is driven with a 100µA current called Ι P. Another analog current Ι F, with 5mA maximum drive proportional to the voltage across the CCP1 is applied at the same node. The voltage at the LFA node is VLFA_VCC - 500( Ι P+ Ι F) at any time. Because of the integrator, Ι F changes very slowly, whereas Ι P could change at the positive edge of the data transition as often as a clock period. In the locked position, the average voltage at the LFA (VLFA_VCC – 500( Ι P/2+ Ι F)) is such that VCO generates frequency ƒ, equal to the data rate clock frequency. Since Ι P is changing all the time between 0A and 100µA, there will be two levels generated at the LFA output. VCO The GO1515 is an external hybrid VCO, which has a centre frequency of 1.485GHz and is also guaranteed to provide 1.485/1.001GHz within the control voltage (3.1V – 4.65V) of the GS1515 over process, power supply and temperature. The GO1515 is a very clean frequency source and because of the internal high Q resonator, it is an order of magnitude more immune to external noise as compared to on-chip VCOs. The VCO gain, Kƒ, is nominally 16MHz/V. The control voltage around the average LFA voltage will be 500 x Ι P/2. This will produce two frequencies off from the centre by ƒ=Kƒ x 500 x Ι P/2. LOOP BANDWIDTH OPTIMIZATION Since the feed back loop has only digital circuits, the small signal analysis does not apply to the system. The effective loop bandwidth scales with the amount of input jitter modulation index. The following table summarizes the relationship between input jitter modulation index and bandwidth when RCP1 and CCP3 are not used. See the Typical Application Circuit artwork for the location of RCP1 and CCP3. The product of the input jitter modulation (IJM) and the bandwidth (BW) is a constant. In this case, it is 282.9kHzUI. The loop bandwidth automatically reduces with increasing input jitter, which helps in cleaning up the signal as much as possible. Using a series combination of RCP1 and CCP3 in parallel to an on-chip resistor (as shown in the Typical Application Circuit) can reduce the loop bandwidth of the GS1515. The parallel combination of the resistor is directly proportional to the bandwidth factor. For example, the on-chip 500 Ω resistor yields 282.9kHzUI. If a 50 Ω resistor is connected in parallel, the effective resistance will be (50 || 500) 45.45 Ω. This resistance yields a bandwidth factor of [282.9 X (45.45/500)] = 25.72kHzUI. The capacitance CCP3 in series with the RCP1 should be chosen such that the RC factor is 50µF. For example, RCP1=50 Ω would require CCP3=1µF. The synchronous lock time increases with reduced bandwidth. Nominal synchronous lock time is equal to [ /Bandwidth factor]. That is, the default bandwidth factor (282.9kHzUI) would yield 1.25µs. For 25.72kHzUI, the synchronous lock time is 0.3535/25.72k=13.75µs. Since the CCP1, CCP2 and CCP3 are also charged, it is measured to be about 11µs which is slightly less than the calculated value of 13.75µs. The Kƒ of the VCO (GO1515) is specified with a minimum of 11MHz/V and maximum of 21MHz/V which is about ±32% variation. The 500 x Ι P/2 will vary about ±10%. The resulting bandwidth factor would approximately vary by ±45% when no RCP1 and CCP3 are used. Ι P by itself may vary by 30% so the variability for lower bandwidths will increase by an additional ±30%. The CCP1 and CCP2 capacitors should be changed with reduced bandwidths. Smaller CCP1 and CCP2 capacitors would result in jitter peaking, lower stability, less probability of locking but at the same time lowering the asynchronous INPUT JITTER MODULATION INDEX BANDWIDTH BW JITTER FACTOR (jitter modulation x BW) 0.05 5.657MHz 282.9kHzUI 0.10 2.828MHz 282.9kHzUI 0.20 1.414MHz 282.9kHzUI 0.50 565.7kHz 282.9kHzUI 0.25 2 × |
Аналогичный номер детали - GS1515-CQM |
|
Аналогичное описание - GS1515-CQM |
|
|
ссылки URL |
Конфиденциальность |
ALLDATASHEETRU.COM |
Вашему бизинису помогли Аллдатащит? [ DONATE ] |
Что такое Аллдатащит | реклама | контакт | Конфиденциальность | обмен ссыками | поиск по производителю 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 |