Datasheet LT1713, LT1714 (Analog Devices) - 12
| Manufacturer | Analog Devices |
| Description | Single/Dual, 7ns, Low Power, 3V/5V/±5V Rail-to-Rail Comparators |
| Pages / Page | 16 / 12 — TYPICAL APPLICATIO S. Figure 4. Performance of Figure 3’s Circuit When. … |
| File Format / Size | PDF / 239 Kb |
| Document Language | English |
TYPICAL APPLICATIO S. Figure 4. Performance of Figure 3’s Circuit When. Figure 5. Performance When Operated Simultaneous
Model Line for this Datasheet
Text Version of Document
LT1713/LT1714
U TYPICAL APPLICATIO S
171112 F04 171112 F05
Figure 4. Performance of Figure 3’s Circuit When Figure 5. Performance When Operated Simultaneous Operated Unidirectionally. Eye is Wide Open Bidirectionally (Full Duplex). Crosstalk Appears as Noise. Eye is Slightly Shut But Performance is Still Excellent
This amounts to an attenuation factor of 0.0978 with the The LT1713 is set up as a crystal oscillator. The varactor values shown. (The actual voltage on the lines will be cut diode is biased from the tuning input. The tuning network in half again due to the 120Ω ZO.) The reason this is arranged so a 0V to 5V drive provides a reasonably attenuation factor is important is that it is the key to symmetric, broad tuning range around the 14.31818MHz deciding the ratio between the R2-R3 resistor divider in center frequency. The indicated selected capacitor sets the receiver path. This divider allows the receiver to reject tuning bandwidth. It should be picked to complement loop the large signal of the local transmitter and instead sense response in phase locking applications. Figure 6 is a plot the attenuated signal of the remote transmitter. Note that of tuning input voltage versus frequency deviation. Tuning in the above equations, R2 and R3 are not yet fully deviation from the 4 × NTSC 14.31818MHz center fre- determined because they only appear as a sum. This quency exceeds ±240ppm for a 0V to 5V input. allows the designer to now place an additional constraint 1 Using the design value of R2 + R3 = 2.653k rather than the implementation value of 2.55k + on their values. The R2-R3 divide ratio should be set to 124Ω = 2.674k. equal half the attenuation factor mentioned above or: R3/R2 = 1/2 • 0.09761. 9 14.3217MHz 8 Having already designed R2 + R3 to be 2.653k (by allocat- 7 ing input impedance across RO, R1 and R2 + R3 to get the 6 requisite 120Ω), R2 and R3 then become 2529Ω and 123.5Ω respectively. The nearest 1% value for R2 is 2.55k 5 14.31818MHz and that for R3 is 124Ω. 4 3
Voltage-Tunable Crystal Oscillator
2 FREQUENCY DEVIATION (kHz) 1 The front page application is a variant of a basic crystal 14.314.0MHz 0 oscillator that permits voltage tuning of the output fre- 0 1 2 3 4 5 quency. Such voltage-controlled crystal oscillators (VCXO) INPUT VOLTAGE (V) are often employed where slight variation of a stable 171112 F06 carrier is required. This example is specifically intended to
Figure 6. Control Voltage vs Output Frequency for the First Page
provide a 4 × NTSC sub-carrier tunable oscillator suitable
Application Circuit. Tuning Deviation from Center Frequency
for phase locking.
Exceeds
±
240ppm
12
U TYPICAL APPLICATIO S
171112 F04 171112 F05
Figure 4. Performance of Figure 3’s Circuit When Figure 5. Performance When Operated Simultaneous Operated Unidirectionally. Eye is Wide Open Bidirectionally (Full Duplex). Crosstalk Appears as Noise. Eye is Slightly Shut But Performance is Still Excellent
This amounts to an attenuation factor of 0.0978 with the The LT1713 is set up as a crystal oscillator. The varactor values shown. (The actual voltage on the lines will be cut diode is biased from the tuning input. The tuning network in half again due to the 120Ω ZO.) The reason this is arranged so a 0V to 5V drive provides a reasonably attenuation factor is important is that it is the key to symmetric, broad tuning range around the 14.31818MHz deciding the ratio between the R2-R3 resistor divider in center frequency. The indicated selected capacitor sets the receiver path. This divider allows the receiver to reject tuning bandwidth. It should be picked to complement loop the large signal of the local transmitter and instead sense response in phase locking applications. Figure 6 is a plot the attenuated signal of the remote transmitter. Note that of tuning input voltage versus frequency deviation. Tuning in the above equations, R2 and R3 are not yet fully deviation from the 4 × NTSC 14.31818MHz center fre- determined because they only appear as a sum. This quency exceeds ±240ppm for a 0V to 5V input. allows the designer to now place an additional constraint 1 Using the design value of R2 + R3 = 2.653k rather than the implementation value of 2.55k + on their values. The R2-R3 divide ratio should be set to 124Ω = 2.674k. equal half the attenuation factor mentioned above or: R3/R2 = 1/2 • 0.09761. 9 14.3217MHz 8 Having already designed R2 + R3 to be 2.653k (by allocat- 7 ing input impedance across RO, R1 and R2 + R3 to get the 6 requisite 120Ω), R2 and R3 then become 2529Ω and 123.5Ω respectively. The nearest 1% value for R2 is 2.55k 5 14.31818MHz and that for R3 is 124Ω. 4 3
Voltage-Tunable Crystal Oscillator
2 FREQUENCY DEVIATION (kHz) 1 The front page application is a variant of a basic crystal 14.314.0MHz 0 oscillator that permits voltage tuning of the output fre- 0 1 2 3 4 5 quency. Such voltage-controlled crystal oscillators (VCXO) INPUT VOLTAGE (V) are often employed where slight variation of a stable 171112 F06 carrier is required. This example is specifically intended to
Figure 6. Control Voltage vs Output Frequency for the First Page
provide a 4 × NTSC sub-carrier tunable oscillator suitable
Application Circuit. Tuning Deviation from Center Frequency
for phase locking.
Exceeds
±
240ppm
12
