EURO QUARTZ APPLICATION NOTES Oscillator Circuits Page 1 of 4 Schmitt Trigger Crystal Oscillator IC-Compatible Oscillator Circuit On/off Control R2 560 R1 560 2k 2k 0.1 1.5k 1 C2 7414 1.5k Output 0.01 2 Xtal 2 ~ 10MHz Schmitt Trigger Crystal Oscillator IC-Compatible Oscillator Circuit In this circuit, resistors R1 and R2 temperature-stabilise the NAND gates, and ensure that the gates are in a linear region for start-up. Capacitor C1 is a DC block and must have <0.1Ω impedance at the operating frequency. The crystal runs in series mode, so it is important that its series resistance is low. AT-cut crystals in the range 1MHz to 10MHz work well, giving a duty cycle of nearly 50%, with chip-limited rise times. The circuit starts well from 0° to 70°C. A Schmitt trigger provides good squaring of the output, and sometimes eliminates the need for an extra output stage. To prevent spurious oscillation ensure C2 = 1/1x104 (frequency is in Hz.) Overtone Oscillator 50MHz ~ 100MHz 0.01 4.7k C2 Xc=100 L1 XL=100 C1 C3 +5 to =12VDC Output Sine Wave 2N918 Low-Noise Crystal Oscillator 0.01 100 2N918 10k 2.2k 390p 0.001u Ca 4MHz L2 0 Volts Overtone Oscillator 50MHz ~ 100MHz 10k 22 330 12V 200mV/22 2.2n 4.7k 2.2n Low-Noise Crystal Oscillator This oscillator delivers an output of high spectral purity without degrading stability. In addition to determining the oscillator frequency, the crystal is also used as a low-pass filter for the unwanted harmonics and as a bandpass filter for the sideband noise. The noise bandwidth is less than 100Hz. All higher harmonics are suppressed -60dB down for the third harmonic of the 4MHz fundamental oscillator frequency. In this circuit the crystal is AT-cut and operates in overtone mode. L1 and C2 are tuned to the operating frequency, while L2 and the shunt capacitance of the crystal should resonate at the oscillator output frequency. (For example, L2 is approximately 0.5µH at 90MHz. This is necessary to tune out the crystal C0.) C3 is adjusted to match the oscillator output. Precision Clock Generator +5V O/P 1 10MHz ICM7209 O/P 2 (f/8) 6~36p 10MHz 1.25MHz 20p Disable Precision Clock Generator The CMOS IC directly drives 5 TTL loads from either of two buffered outputs. The device operates to 10MHz and is bipolar, MOS and CMOS compatible. EUROQUARTZ LIMITED Blacknell Lane CREWKERNE Somerset UK TA18 7HE Tel: +44 (0)1460 230000 Fax: +44 (0)1460 230001 [email protected] www.euroquartz.co.uk EURO QUARTZ APPLICATION NOTES Page 2 of 4 CMOS Crystal Oscillator Fundamental Frequency Crystal Oscillator 2~60pF Output Rp 5 1.0k Rp 10 3 9 4 2 510 7 13 Rp 6 510 15 12 14 Rp Rp R1 Out 22M Vee 0.1uF C1 22p IC = MC10116 Vbb in MC10116 IC = NOR 4001 Out R2 22k C2 40p Rp = 510 W to Vee or 50 W to Vtt Fundamental Frequency Crystal Oscillator CMOS Crystal Oscillator For frequencies below 20MHz, a fundamental frequency crystal can be used and the resonant tank is no longer required. Also at this lower frequency range the typical MECL 10,000 propagation delay of 2ns becomes small compared to the period of oscillation, and it is necessary to use a non-inverting output. Therefore the MC10116 oscillator section functions simply as an amplifier. The 1.0kΩ resistor biases the line receiver near Vss and the 0.1µF capacitor is a filter capacitor for the Vbb supply. The capacitor, in series with the crystal, provides for minor frequency adjustments. The second section of the MC10116 is connected as a Schmitt-trigger circuit, ensuring good MECL edges from a slow, less than 20MHz input signal. The third stage of the MC10116 is used as a buffer and to give complementary outputs from the crystal oscillator circuit. The circuit has a maximum operating frequency of approximately 20MHz and a minimum of approximately 1MHz. Use a fundamental mode crystal. This circuit has a frequency range of 0.5MHz to 2.0MHz. The frequency can be adjusted to a precise value with trimmer capacitor C2. The second NOR gate serves as an output buffer. Temperature-Compensated Crystal Oscillator +5VDC 0.05 10k 470 33k 470 Output Easy Start-up Crystal Oscillator 01 C1 C2 C3 Output R1 G1 10k 680 C4 R2 G2 G3 510 510 C1 47pF C2 47pF G4 Temperature-Compensated Crystal Oscillator Easy Start-up Crystal Oscillator This is a low-cost, crystal-controlled oscillator using one TTL gate. Start-up is ensured by the connection of NAND gates G1, G2 and G3 into an unstable logic configuration and the high loop gain of the three inverters. Select the values of R1, R2, C1 and C2 so the oscillator operates at a frequency 70% to 90% higher than required with the crystal disconnected. For 1MHz to 2MHz operation a lowpower 54L00 IC is recommended; for 2MHz to 6MHz, a standard 5400 type, and for 6MHz to 50MHz a 54H00 or 54S00. For a 5MHz AT-cut crystal, C = 3pF to 8pF (fine frequency trimmer) C2 = 4pF to 24pF N500 (temperature compensating) C3 = 8pF to 48pF N1500 (temperature compensating) and C4 = 120pF silver mica. The different negative-coefficient capacitors are blended to produce the desired change in capacitance to counteract or compensate for the decrease in frequency of the ‘normal’ AT-cut characteristics of the crystal. EUROQUARTZ LIMITED Blacknell Lane CREWKERNE Somerset UK TA18 7HE Tel: +44 (0)1460 230000 Fax: +44 (0)1460 230001 [email protected] www.euroquartz.co.uk EURO QUARTZ APPLICATION NOTES Page 3 of 4 Overtone Crystal Oscillator Overtone Crystal Oscillator 12V C3 10p 1000 Output L2 C1 C2 5p R1 120 560 1000 L1 81 x 0.25mm dia 10k +12VDC C4 .01u 1.5uH Ferrite Bead 120 4.7 22k 0.47u 5.1 Rf out 4.3 1.5k 180 1-10 33 Overtone Crystal Oscillator Overtone Crystal Oscillator The crystal in this circuit is connected directly between the base and ground of the transistor. Capacitor C1 is used to improve the feedback due to the internal capacitances of the transistor. This capacitor should be mounted as close as possible to the case of the transistor. The LC tank circuit in the collector of the transistor is tuned to the overtone frequency of the crystal. The emitter resistor capacitor must have a capacitive reactance of approximately 90Ω at the frequency of operation. The tap on inductor L1 is used to match the impedance of the transistor collector. Usually, the placement of this tap is approximately one third from the cold end of the coil. The placement of the trap is a trade-off between stability and maximum power output. The output signal is taken from a link coupling coil, L2 and operates by transformer action. This design gives high reliability over a wide temperature range and uses fifth and seventh overtone crystals. The inductor in parallel with the crystal causes anti-resonance of the crystal C0 to minimize loading. This is a common technique with overtone crystals. Voltage-Controlled Crystal Oscillator MV2108 2-60pF R2 R1 510k 5 3 4 2 Rp 1.0k 10 510 VXO Crystal Oscillator 0.1uF 390k 11 Vbb in MC10116 Vr 0.1uF Xc<10 7 13 15 6 12 14 Rp Out Out Rp 9 1629 mH 100k Rp Rp 510 IC=MC10116 Rp = 510 W to Vee or 50W to Vtt 100 2k7 100 0.01 24k 0.01 390 2.5mH 1k Nominal Frequency MHz 1.000 1.8432 10.000 15.000 Deviation +ppm -ppm 57.0 48.0 95.5 80.3 197.4 202.8 325.4 322.9 0.01 Voltage-Controlled Crystal Oscillator VXO Crystal Oscillator This circuit provides a stable VXO using 6MHz or 8MHz crystals. Frequency pulling on either side of series resonance is achieved by use of the capacitor and inductor. A voltage-variable capacitance tuning diode is placed in series with the crystal feedback path. Changing the voltage on Vr varies the tuning diode capacitance and tunes the oscillator. The 510kΩ resistor, R1, establishes a reference voltage from the feedback loop and 0.1µF cap. C2 provides AC coupling to the tuning diode. The circuit operates over a tuning range of 0 to 25V. It is possible to change the tuning range from 0 to 25V by reversing the tuning diode D1.Centre frequency is set with the 2-60pF trimmer capacitor. The table above shows measured deviation for several tested crystals. EUROQUARTZ LIMITED Blacknell Lane CREWKERNE Somerset UK TA18 7HE Tel: +44 (0)1460 230000 Fax: +44 (0)1460 230001 [email protected] www.euroquartz.co.uk EURO QUARTZ APPLICATION NOTES Page 4 of 4 Overtone Crystal Oscillator Crystal Timebase C2 C1 47pF 9~35pF 5 3 10 7 4 2 9 6 +Vcc Out Out C1 9~35pF 1 L1 Rp Rp 8 6 IC1 MM5369 5 12 2 C3 0.1uF Vbb 1 11 Vbb in MC10116 0.001uF Rp L1 = 0.33uH for 50 ~ 100MHz L1 = 1.0uH for 20 ~ 50MHz Rp = 510 W to Vee or 50 W to Vtt S1 Reset R2 22k 2 R1 20M +Vcc 9 10 14 13 11 IC3a +Vcc 14 11 9 6 5 4 IC2 4824 1/2 4012 12 5 1 sec. 0.1 sec 4 3 IC3b 2 S2 7 7 11 13 IC4a 1/2 4012 12 1/4 4811 C3 1uF Overtone Crystal Oscillator This circuit uses an adjustable resonant tank circuit to ensure operation at the desired crystal overtone. C1 and L1 form the resonant tank circuit, which, with the values specified as a resonant frequency, are adjustable from approximately 50MHz to 100MHz. Overtone operation is accomplished by adjusting the tank circuit frequency at or near the desired frequency. The tank circuit exhibits a low impedance shunt to off-frequency oscillations and a high impedance to the desired frequency, which allows feedback from the output. Operation in this manner guarantees that the oscillator will always start at the correct overtone. 3.58MHz +V C2 47pF +Vcc Timebase output 22k IC4b IC4c IC4d Reset Output Crystal Timebase An on-board oscillator and a 17 stage divider compose IC1. By connecting a standard 3.58MHz, television colour-burst crystal as shown, an accurate source of 60Hz squarewaves is generated at the ICs output, pin 1. Those pulses are then fed to IC2, a 4024 sevenstage ripple counter. Its outputs are connected directly to different gates in IC3, which is a dual four-input NAND gate. Depending upon which position pulse-select switch S2 occupies, one of those gates will provide an output/reset pulse of the selected width. EUROQUARTZ LIMITED Blacknell Lane CREWKERNE Somerset UK TA18 7HE Tel: +44 (0)1460 230000 Fax: +44 (0)1460 230001 [email protected] www.euroquartz.co.uk