PS20353 Datasheet, PDF (23/27 Pages) List of Unclassifed Manufacturers – Nordig Unified DVB-T COFDM Terrestrial Demodulator

PS20353
Typical load capacitance
Drive level
Equivalent series resistance
Figure 14 - Crystal Oscillator Circuit
XTI
XTI
20 pF
0.4 mW max
<40 Ω
XT0
OSCMODE
C1
C2
4.5.1 Selection of External Components
The capacitor values used must ensure correct operation of the Pierce oscillator such that the total loop gain is
greater than unity. Correct selection of the two capacitors is very important and the following method is
recommended to obtain values for C1 and C2. Alternatively there is a calculator available (ZLAN-125) that will
calculate the external component values for you.
4.5.1.1
Loop Gain Equation
Although oscillation may still occur if the loop gain is just above 1, a loop gain of between 5 and 25 is optimum to
ensure that oscillations will occur across all variations in temperature, process and supply voltage, and that the
circuit will exhibit good start-up characteristics.
Equation 1 -
Equation 2 -
4.5.1.2
List of Equation Parameters
A
Cin
Cout
Cpar
Zo
gm
Rf
ESR
f
total loop gain (between 5 and 25)
C1 + Cpar
C2 + Cpar
parasitic capacitance associated with each oscillator pin (XTI and XTO). It consists of track capacitances,
package capacitance and cell input capacitance. Normally Cpar ≈ 4pF.
9.143kΩ - output impedance of amplifier at 1.8V operation - typical
8.736mA/V - transconductance of amplifier at 1.8V operation -typical
2.3MΩ - internal feedback resistor
maximum equivalent series resistance of crystal - given by crystal manufacturer (Ω)
fundamental frequency of crystal (Hz)
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