MC54HC4060J データシートの表示（PDF） - Motorola => Freescale
部品番号
コンポーネント説明
メーカー
MC54HC4060J Datasheet PDF : 10 Pages
| |||
MC54/74HC4060
DESIGN PROCEDURES
The following procedure applies for oscillators operating below 2 MHz where Z is a resistor R1. Above 2 MHz, additional im-
pedance elements should be considered: Cout and Ca of the amp, feedback resistor Rf, and amplifier phase shift error from 180_.
Step 1: Calculate the equivalent series circuit of the crystal at the frequency of oscillation.
Ze
=
– jXCo (Rs + jXLs – jXCs
– jXCo + Rs + jXLs – jXCs
= Re + jXe
Reactance jXe should be positive, indicating that the crystal is operating as an inductive reactance at the oscillation frequency
The maximum Rs for the crystal should be used in the equation.
Step 2: Determine β, the attenuation, of the feedback network. For a closed–loop gain of 2, Aνβ = 2,β = 2/Aν where Aν is
the gain of the HC4060 amplifier.
Step 3: Determine the manufacturer’s loading capacitance. For example: A manufacturer may specify an external load capaci-
tance of 32 pF at the required frequency.
Step 4: Determine the required Q of the system, and calculate Rload. For example, a manufacturer specifies a crystal Q
of 100,000. In–circuit Q is arbitrarily set at 20% below crystal Q or 80,000. Then Rload = (2πfoLs/Q) – Rs where Ls and Rs are
crystal parameters.
Step 5: Simultaneously solve, using a computer,
β=
XC • XC2
(with feedback phase shift = 180_)
(1)
R • Re + XC2 (Xe – XC)
Xe = XC2 + XC + ReXC2 = XCload (where the loading capacitor is an external load, not including Co)
(2)
R
Rload =
RXCoXC2[(XC + XC2) (XC + XCo) – XC(XC + XCo + XC2)]
X2C2(XC + XCo)2 + R2(XC + XCo + XC2)2
(3)
Here R = Rout + R1. Rout is amp output resistance, R1 is Z. The C corresponding to XC is given by C = C1 + Cin.
Alternately, pick a value for R1 (i.e., let R1 = Rs). Solve Equations 1 and 2 for C1 and C2. Use Equation 3 and the fact that
Q = 2πfoLs/(Rs + Rload) to find in–circuit Q. If Q is not satisfactory pick another value for R1 and repeat the procedure.
CHOOSING R1
Power is dissipated in the effective series resistance of the
crystal. The drive level specified by the crystal manufacturer
is the maximum stress that a crystal can withstand without
damage or excessive shift in frequency R1 limits the drive
level.
To verify that the maximum dc supply voltage does not
overdrive the crystal, monitor the output frequency as a func-
tion of voltage at Osc Out 2 (Pin 9). The frequency should
increase very slightly as the dc supply voltage is increased.
An overdriven crystal will decrease in frequency or become
unstable with an increase in supply voltage. The operating
supply voltage must be reduced or R1 must be increased in
value it the overdriven condition exists. The user should note
that the oscillator start–up time is proportional to the value of
R1.
SELECTING Rf
The feedback resistor, Rf, typically ranges up to 20 MΩ. Rf
determines the gain and bandwidth of the amplifier. Proper
bandwidth insures oscillation at the correct frequency plus
roll–off to minimize gain at undesirable frequencies, such as
the first overtone. Rf must be large enough so as to not affect
the phase of the feedback network in an appreciable manner.
ACKNOWLEDGEMENTS AND RECOMMENDED
REFERENCES
The following publications were used in preparing this data
sheet and are hereby acknowledged and recommended for
reading:
Technical Note TN–24, Statek Corp.
Technical Note TN–7, Statek Corp.
D. Babin, “Designing Crystal Oscillators”, Machine Design,
March 7, 1985.
D. Babin, “Guidelines for Crystal Oscillator Design”,
Machine Design, April 25, 1985.
ALSO RECOMMENDED FOR READING:
E. Hafner, “The Piezoelectric Crystal Unit – Definitions and
Method of Measurement”, Proc. IEEE, Vol. 57, No. 2, Feb.
1969.
D. Kemper, L. Rosine, “Quartz Crystals for Frequency
Control”, Electro–Technology, June, 1969.
P. J. Ottowitz, “A Guide to Crystal Selection”, Electronic
Design, May, 1966.
High–Speed CMOS Logic Data
7
DL129 — Rev 6
MOTOROLA
Share Link: 