Datasheet LT1711, LT1712 (Analog Devices) - 10
| Hersteller | Analog Devices |
| Beschreibung | Single/Dual 4.5ns, 3V/5V/±5V, Rail-to-Rail Comparators |
| Seiten / Seite | 12 / 10 — TYPICAL APPLICATIO S. Figure 4. Performance of Figure 3’s Circuit When. … |
| Dateiformat / Größe | PDF / 226 Kb |
| Dokumentensprache | Englisch |
TYPICAL APPLICATIO S. Figure 4. Performance of Figure 3’s Circuit When. Figure 5. Performance When Operated Simultaneous
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Textversion des Dokuments
LT1711/LT1712
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 comes out to 120Ω for the values shown. The are often employed where slight variation of a stable Thevenin equivalent source voltage is given by: carrier is required. This example is specifically intended to provide a 4 × NTSC sub-carrier tunable oscillator suitable R ( 2 R3 – R ) 1 V = + V for phase locking. TH S • R ( 2 + R3 + R ) 1 The LT1711 is set up as a crystal oscillator. The varactor RO • diode is biased from the tuning input. The tuning network R + 2 • R [ |1| R(2+R3 ] O ) is arranged so a 0V to 5V drive provides a reasonably This amounts to an attenuation factor of 0.0978 with the symmetric, broad tuning range around the 14.31818MHz values shown. (The actual voltage on the lines will be cut center frequency. The indicated selected capacitor sets in half again due to the 120Ω Z tuning bandwidth. It should be picked to complement loop O.) The reason this attenuation factor is important is that it is the key to response in phase locking applications. Figure 6 is a plot deciding the ratio between the R2-R3 resistor divider in of tuning input voltage versus frequency deviation. Tuning the receiver path. This divider allows the receiver to reject deviation from the 4 × NTSC 14.31818MHz center fre- the large signal of the local transmitter and instead sense quency exceeds ±240ppm for a 0V to 5V input. the attenuated signal of the remote transmitter. Note that 1 Using the design value of R2 + R3 = 2.653k rather than the implementation value of 2.55k + 124Ω = 2.674k. in the above equations, R2 and R3 are not yet fully determined because they only appear as a sum. This 9 14.3217MHz allows the designer to now place an additional constraint 8 on their values. The R2-R3 divide ratio should be set to 7 equal half the attenuation factor mentioned above or: 6 R3/R2 = 1/2 • 0.09761. 5 14.31818MHz 4 Having already designed R2 + R3 to be 2.653k (by allocat- 3 ing input impedance across RO, R1 and R2 + R3 to get the 2 requisite 120Ω), R2 and R3 then become 2529Ω and FREQUENCY DEVIATION (kHz) 1 123.5Ω respectively. The nearest 1% value for R2 is 2.55k 14.3140MHz 0 and that for R3 is 124Ω. 0 1 2 3 4 5 INPUT VOLTAGE (V)
Voltage-Tunable Crystal Oscillator
171112 F06
Figure 6. Control Voltage vs Output Frequency for the
The front page application is a variant of a basic crystal
Front Page Application Circuit. Tuning Deviation from
oscillator that permits voltage tuning of the output fre-
Center Frequency Exceeds
±
240ppm
quency. Such voltage-controlled crystal oscillators (VCXO) 10
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 comes out to 120Ω for the values shown. The are often employed where slight variation of a stable Thevenin equivalent source voltage is given by: carrier is required. This example is specifically intended to provide a 4 × NTSC sub-carrier tunable oscillator suitable R ( 2 R3 – R ) 1 V = + V for phase locking. TH S • R ( 2 + R3 + R ) 1 The LT1711 is set up as a crystal oscillator. The varactor RO • diode is biased from the tuning input. The tuning network R + 2 • R [ |1| R(2+R3 ] O ) is arranged so a 0V to 5V drive provides a reasonably This amounts to an attenuation factor of 0.0978 with the symmetric, broad tuning range around the 14.31818MHz values shown. (The actual voltage on the lines will be cut center frequency. The indicated selected capacitor sets in half again due to the 120Ω Z tuning bandwidth. It should be picked to complement loop O.) The reason this attenuation factor is important is that it is the key to response in phase locking applications. Figure 6 is a plot deciding the ratio between the R2-R3 resistor divider in of tuning input voltage versus frequency deviation. Tuning the receiver path. This divider allows the receiver to reject deviation from the 4 × NTSC 14.31818MHz center fre- the large signal of the local transmitter and instead sense quency exceeds ±240ppm for a 0V to 5V input. the attenuated signal of the remote transmitter. Note that 1 Using the design value of R2 + R3 = 2.653k rather than the implementation value of 2.55k + 124Ω = 2.674k. in the above equations, R2 and R3 are not yet fully determined because they only appear as a sum. This 9 14.3217MHz allows the designer to now place an additional constraint 8 on their values. The R2-R3 divide ratio should be set to 7 equal half the attenuation factor mentioned above or: 6 R3/R2 = 1/2 • 0.09761. 5 14.31818MHz 4 Having already designed R2 + R3 to be 2.653k (by allocat- 3 ing input impedance across RO, R1 and R2 + R3 to get the 2 requisite 120Ω), R2 and R3 then become 2529Ω and FREQUENCY DEVIATION (kHz) 1 123.5Ω respectively. The nearest 1% value for R2 is 2.55k 14.3140MHz 0 and that for R3 is 124Ω. 0 1 2 3 4 5 INPUT VOLTAGE (V)
Voltage-Tunable Crystal Oscillator
171112 F06
Figure 6. Control Voltage vs Output Frequency for the
The front page application is a variant of a basic crystal
Front Page Application Circuit. Tuning Deviation from
oscillator that permits voltage tuning of the output fre-
Center Frequency Exceeds
±
240ppm
quency. Such voltage-controlled crystal oscillators (VCXO) 10