Pierce Oscillator
Design and Crystal
Recommendations
Oscillator Design Check
TDC-GP22
Osc. In
Osc. Out
RF
RD
32.768 kHz
XTAL
CG
Acam
TDC-GP22
CD
Test Conditions
Power Supply Voltage VDD
Load Capacitors CD / CG
Feedback Resistor RF
Serial Resistor RD
Results
Effective Load Capacitance
Oscillation Allowance
Oscillator Output Voltage AC
Drive Level
Startup Time
Overtone Mode Suppression
6.0
9/9
10
0
V
pF
M
k
7.21
>500
306
0.064
120
Safe
pF
k
mVRMS
W
ms
----
Recommendation
Crystal
Crystal Type
CM8V-T1A
Frequency
32.768
Load Capacitance CL
7.0
Tolerance
+/-20
Oscillator Design
RF
10
RD
0
CD
9
CG
9
kHz
pF
ppm
M
k
pF
pF
Remarks
The TDC-GP22 consists of a self-limiting low power Pierce Oscillator.
Placing CD = 9 pF and CG = 9 pF load capacitors on each side of the crystal results in an effective load
capacitance of 7.2 pF (including board stray capacitances) which is a good match for a crystal specified for CL
= 7.0 pF.
The oscillator circuit provides an oscillation allowance greater than 500 k; this allows the safe use of smallest
SMD quartz crystals (ESR  100 k).
Date: February 2016
Revision N°: 1.0
Page 1/3
In accordance with our policy of continuous development and improvement,
Micro Crystal reserves the right to modify specifications or design-recommendations without prior notice.
The recommendations stated above are based on measured-results, respecting the “oscillator design rules”.
Micro Crystal makes no representation or warranty for information in this “Design and Crystal Recommendations”.
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Email
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Pierce Oscillator
Design and Crystal
Recommendations
Acam
TDC-GP22
Crystal Input and Output waveforms (VDD = 6.0 V):
C1: Osc. Out (200 mV/div - AC)
C2: Osc. In (200 mV/div - AC)
Time base: 10 s/div
Oscillator Output startup waveform (VDD = 6.0 V):
C1: Osc. Out (200 mV/div - DC)
Time base: 50 ms/div
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Pierce Oscillator
Design and Crystal
Recommendations
Acam
TDC-GP22
Crystal matching chart:
Acam - TDC-GP22
Design Settings: CD = 9 pF / CG = 9 pF / RF = 10 M
Effective Load Capacitance: 7.2 pF
32780
360.00
32779
330.00
32778
32777
Frequency FL
CL dependent
Frequency / Hz
32775
270.00
240.00
210.00
32774
180.00
32773
150.00
32772
120.00
32771
90.00
Frequency
Shift: -5.8 ppm
32770
60.00
32769
30.00
32768
0.00
32767
-30.00
32766
-60.00
Frequency
Target
32765
Delta F/F / ppm
32776
300.00
Oscillator's Effective
Load Capacitance
CLoad: 7.2 pF
-90.00
32764
-120.00
Crystal Specification
CL: 7.0 pF
32763
32762
-150.00
-180.00
32761
-210.00
32760
-240.00
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Load Capacitance / pF
As shown in the chart above, an effective load capacitance of 7.2 pF results in a frequency offset of
-5.8 ppm using a CM8V-T1A crystal specified for CL: 7.0 pF.
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