Application notes

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 info@euroquartz.co.uk 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 info@euroquartz.co.uk 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 info@euroquartz.co.uk 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 info@euroquartz.co.uk www.euroquartz.co.uk