Datenblatt-Suchmaschine für elektronische Bauteile |
|
CD74HCT7046AM96 Datenblatt(PDF) 4 Page - Texas Instruments |
|
|
CD74HCT7046AM96 Datenblatt(HTML) 4 Page - Texas Instruments |
4 / 28 page 4 quency is lower than the COMPIN frequency, then it is the n- type driver that is held “ON” for most of the cycle. Subse- quently, the voltage at the capacitor (C2) of the low-pass filter connected to PC2OUT varies until the signal and comparator inputs are equal in both phase and frequency. At this stable point the voltage on C2 remains constant as the PC2 output is in three-state and the VCO input at pin 9 is a high impedance. Thus, for PC2, no phase difference exists between SIGIN and COMPIN over the full frequency range of the VCO. Moreover, the power dissipation due to the low-pass filter is reduced because both p-type and n-type drivers are “OFF” for most of the signal input cycle. It should be noted that the PLL lock range for this type of phase comparator is equal to the capture range and is independent of the low-pass filter. With no signal present at SIGIN, the VCO adjusts, via PC2, to its lowest frequency. Lock Detector Theory of Operation Detection of a locked condition is accomplished by a NOR gate and an envelope detector as shown in Figure 6. When the PLL is in Lock, the output of the NOR gate is High and the lock detector output (Pin 1) is at a constant high level. As the loop tracks the signal on Pin 14 (signal in), the NOR gate outputs pulses whose widths represent the phase differ- ences between the VCO and the input signal. The time between pulses will be approximately equal to the time con- stant of the VCO center frequency. During the rise time of the pulse, the diode across the 1.5k Ω resistor is forward biased and the time constant in the path that charges the lock detector capacitor is T = (150 Ω x CLD). During the fall time of the pulse the capacitor discharges through the 1.5k Ω and the 150Ω resistors and the channel resistance of the n-device of the NOR gate to ground (T = (1.5k Ω + 150Ω + Rn-channel) x CLD). The waveform preset at the capacitor resembles a sawtooth as shown in Figure 7. The lock detector capacitor value is determined by the VCO center frequency. The typical range of capacitor for a frequency of 10MHz is about 10pF and for a frequency of 100kHz is about 1000pF. The chart in Figure 8 can be used to select the proper lock detector capacitor value. As long as the loop remains locked and tracking, the level of the sawtooth will not go below the switching thresh- old of the Schmitt-trigger inverter. If the loop breaks lock, the width of the error pulse will be wide enough to allow the saw- tooth waveform to go below threshold and a level change at the output of the Schmitt trigger will indicate a loss of lock, as shown in Figure 9. The lock detector capacitor also acts to filter out small glitches that can occur when the loop is either seeking or losing lock. Note: When using phase comparator 1, the detector will only indicate a lock condition on the fundamental frequency and not on the harmonics, which PC1 will also lock on. If a detec- tion of lock is needed over the harmonic locking range of PC1, then the lock detector output must be OR-ed with the output of PC1. FIGURE 2. PHASE COMPARATOR 1: AVERAGE OUTPUT VOLTAGE vs INPUT PHASE DIFFERENCE: VDEMOUT = VPC1OUT = (VCC/π) (φSIGIN - φCOM- PIN); φDEMOUT = (φSIGIN - φCOMPIN) FIGURE 3. TYPICAL WAVEFORMS FOR PLL USING PHASE COMPARATOR 1, LOOP LOCKED AT fo VCC VDEMOUT (AV) 1/2 VCC 0 0o 90o φ DEMOUT 180o SIGIN COMPIN VCOOUT PC1OUT VCOIN VCC GND CD74HC7046A, CD74HCT7046A |
Ähnliche Teilenummer - CD74HCT7046AM96 |
|
Ähnliche Beschreibung - CD74HCT7046AM96 |
|
|
Link URL |
Privatsphäre und Datenschutz |
ALLDATASHEETDE.COM |
War ALLDATASHEET hilfreich? [ DONATE ] |
Über Alldatasheet | Werbung | Kontakt | Privatsphäre und Datenschutz | Linktausch | Hersteller 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 |