Analog Devices EE168 Application Notes

Engineer To Engineer Note EE-168

Technical Notes on using Analog Devices' DSP components and development tools

a

Using Third Overtone Crystals with the ADSP-218x DSP

Contributed by Larry Hurst August 8, 2002

Contact our technical support by phone: (800) ANALOG-D or e-mail: [e-mail]
Or visit our on-line resources http://www.analog.com/dsp

and http://www.analog.com/dsp/EZAnswers

rd

OT crystal has a lower activity, (i.e.

For these reasons, extra care should be

rd

OT crystal oscillators

Note that there is often no indication,

rd

OT operation verses

rd

OT operation.

Introduction

DSPs frequently require an input clock
frequency (CLKIN) that is over 35MHz.
Unfortunately fundamental mode crystals over
35MHz are not popular and tend to be expensive
and fragile. Packaged clock oscillators cost
considerably more than a crystal so, for some
applications, using a 3
may be a sensible choice.

While the current trend is to incorporate
PLL frequency multiplication into the DSP,
using a low frequency input clock to generate
internal core clocks of several hundred MHz,
there are still occasions when it might be useful
to consider using a 3

This note discusses using readily
available 3

rd

overtone crystals, at frequencies

over 35MHz, with the ADSP-218x family of

rd

overtone (3

rd

OT crystal.

rd

OT) crystal

Second, a 3
requires a higher minimum drive level to start
reliably).

taken when designing 3
and careful testing should be performed over
temperature, voltage and with a representative
batch of crystals to ensure that all parts operate
reliably.

marked on the crystal package, to show that a
crystal is intended for 3
fundamental mode operation. Care should be
taken to determine this information. If a crystal
is used in a traditional (two capacitor
fundamental mode circuit) appears to be
oscillating at approximately one third of the
frequency marked on it’s package, it is very
likely that it is intended for 3

DSPs. A design procedure is developed for
calculating the optimum values for the support
components. This procedure can be extended to
CODECs and other applications requiring input
clocks over 35MHz.

Design Method

When a 3rd OT crystal is chosen, two
additional circuit components must
the traditional parallel, or fundamental mode

be added to

circuit, to force oscillation at the overtone

Cautionary Note

There are a number of cautions that
should be noted when deciding to use a 3
crystal oscillator.

First, a 3

rd

OT crystal normally has a

higher ESR, typically more than twice that of a

rd

OT

frequency marked on the crystal. The added
components consist of a series inductor and
capacitor as shown in Figure 1. If L

and C3 are

1

not added to the circuit, the crystal will oscillate
at its fundamental frequency, which is
approximately

one third of the desired overtone

frequency.

fundamental mode crystal at the same frequency.

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Engineer-to-Engineer Notes.

a

-=5V

-=5V

18

ADSP-218x-/L/M/N DSP

ADSP-218x-/L/M/N DSP

V

V

DDINT

DDINT

GND

GND

18

17

17

L=3.3V

•

•

•

•

L=3.3V
M=2.5V

M=2.5V

C

C

N=1.8V

N=1.8V

4

4

C

C

FB

FB

••

••

••

C

C

IN

IN

GND

GND

12

12

CLKIN XTAL

CLKIN XTAL

C

C

IS

IS

••
C

C

R

R

FB

FB

••

••

13 14

13 14

••

••

••

C

C

FBS

FBS

••
C

C

OS

OS

OUT

OUT

CLKOUT

CLKOUT

V

V

••

CIS, C

CIS, C

ARE STRAY

ARE STRAY

CAPACITANCES

CAPACITANCES

FBS

FBS

, C

, C

OS

OS

••

•

Y

Y

1

C

C

1

1

1

•

C

C

2

2

L

L

1

1

C

C

3

3

16

16

15

15

•

DDEXT

DDEXT

GND

GND

•

17

17

•

•

COMPONENTS

COMPONENTS

ADDED

ADDED

FOR 3

FOR 3

OSCILLATOR

OSCILLATOR

C

C

5

5

RD

RD

OT

OT

-=5V

-=5V
L=3.3V

L=3.3V
M=2.5-3.3V

M=2.5-3.3V
N=1.8-3.3V

N=1.8-3.3V

Figure 1: Schematic of 3rd Overtone Crystal Oscillator

Note that the three capacitors, C

C

, must be ‘RF’ types with low loss dielectrics

3

, C2 and

1

at the frequencies being used. Examples of
capacitors with suitable dielectrics include silver
mica, polystyrene and ceramic NP0.

The inductor, L

, must also be chosen for

1

low RF losses (i.e. high ‘Q’). At these
frequencies and inductance values this usually
means an air core type, although there are some
inductors that use special formulations of iron
dust and/or ferrites that result in high Q. As a
guide, look for an inductor with a Q greater than
30, DC resistance less than 1.0Ω and a self­resonant frequency (SRF) greater than 120MHz.

The crystal’s load capacitance (C

) is

L

required to ensure the crystal operates at the
labeled frequency and will be specified by the
crystal manufacturer. This is usually a ‘standard’
value and 18pF is very common. It is up to the
engineer to choose the correct values for C
C

and L1 in conjunction with the amplifier and

3

, C2,

1

stray PCB capacitance, to provide the correct
load capacitance, C

. C1 and C2 will usually be

L

between 20pF and 70pF.

C

is only required for blocking DC

3

current that would otherwise load the output of
the oscillator. Its value is not critical and a value
of 1nF NP0 should be satisfactory.

with C

The inductor, L

and the stray output capacitance at a

2

, is chosen to resonate

1

frequency fR ≈ ⅔ of the 3rd OT frequency, fOT.
This provides the correct loading reactance for
the crystal and closed loop phase relationship to
start and maintain oscillation. In addition, the
parallel combination of L
an effective capacitance, C
frequency, f

, to correctly load the crystal.

OT

and C2 must provide

1

at the 3rdOT

2EFF

We have the following two equations

with two unknown values, L

2

f

OT

f

R

==

3

2

π

1

and C2 …

1

Equation 1

)( ++

LCCC

12

OSOUT

×

XX

LC

12

f

,@

OT

+

X

C

EFF

XX

2

LC

12

1

Cf

EFFOT

2

Equation 2

==

2

π

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 2 of 11

a

where fR is the actual resonant frequency of L1
combined with the total output capacitance, C
C

and COS. Note that C2 is the actual

OUT

capacitor value used while C
capacitance at f
of C

and L1.

2

The reactance of C

due to the parallel combination

OT

3

is the effective

2EFF

is small enough to be

,

2

ignored. Similarly the contributions of the
feedback capacitances, C

and C

FB

, are very

FBS

small and can be ignored in determining the
required values of C

and L1.

2

With some simple arithmetic
manipulation we have the resulting design
equations for C

and L1 …

2

C++=

2

L++=

1

4

ω

where: ω

2

49

5

Equation 3

5

2

()

2

Equation 4

= 2πfOT

OT

CCC

OSOUTEFF

CCC

OSOUTEFFOT

()

Summarizing, the crystal manufacturer
will specify a total load capacitance for the
crystal. This is the TOTAL value of capacitance
that must appear across the two terminals of the
crystal for the operating frequency to be within
the specified tolerance of the value stamped on
the package. The total capacitance is usually
called the load capacitance, C
of the amplifier input capacitance, C
capacitance, C

and output capacitance, C

FB

, and will consist

L

, feedback

IN

.

OUT

Added to these is the PCB stray
capacitances, C

, C

IS

and COS. Finally we have

FBS

to add the external capacitors C1 and the parallel
combination of C

and L1.

2

Example: Determining External
Load Capacitors, C
Inductor L

Assume a manufacturer specifies a

37.5MHz 3
C

=18pF. For the ADSP-218xM/N oscillator

L

amplifier, typical values are C
7pF and C
capacitances, assume C
C

=1pF. These are all reasonable

FBS

approximations and, in practice, a couple of pF
either way will not make much difference.

To calculate the equivalent capacitance
across the crystal
output capacitances are effectively in series.

Therefore, the amplifier total capacitance,
C

:

AT

For the PCB total capacitance, C

Therefore, total Amplifier and PCB stray
capacitance, C

The total load capacitance is specified by
the crystal manufacturer. In this case, C
18pF. We have 6pF provided by the amplifier in
the DSP and stray PCB capacitance, as noted
above. Hence we have to add another 12pF in
parallel to make a total of 18pF. This
capacitance is provided by C
combination of C2 in parallel with L1.

1

rd

OT crystal with a load capacitance,

= 1pF. For the PCB stray

FB

=2pF, COS=3pF and

IS

, first note that the input and

C

= C

AT

+ CINC

FB

= [1+ 5×7/(5 + 7)]

≈ 4pF

C

PCBT

= C

+ CISCOS/(C

FBS

= [1 + 2×3/(2 + 3)]

≈ 2pF

:

ST

C

= CAT + C

ST

≈ 6pF

, C2 and

1

= 5pF, C

IN

/(C

OUT

IN

+ C

:

PCBT

+ COS)

IS

PCBT

and the

1

OUT

OUT

)

L

=

=

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 3 of 11

a

NOTE: It is most common to make C1
and C
the crystal, the resulting values for C

equal, and, since they are in series across

2

and C

1

2EFF

will each be 24pF, the series combination
making the 12pf required to make-up the
specified total load capacitance.

NOTE that this ‘sleight of hand’
introduction of capacitance C

in place of C2

2EFF

which is the effective capacitance of the parallel
combination of C2 and L1 required to make 24pF
at the 3rd OT frequency.

At this point we have determined the
value of C

- in this example,

1

C

= 24pF

1

From the design equations, 3 & 4, we can
determine the values of C

& L1,

2

= 662.2×10

-9

H

∴L1 = 662.2nH

Checking Calculated Values

To check the effective capacitance of the

C

//L1 combination at fOT, we can use the

2

expression;

1

+

ω

Lj

1



×

2



ω

Lj

1




1

2

×

L

1

C

2

which simplifies to;

EFF

EFF

ω

Cj

=

j

2



1



ω



ω

Cj



−=

CC

22

ω

()

C++=

2

C

2

2

= [9*24 + 4(7+3)]/5 = 51.2pF

49

5

∴C2 = 51.2pF

Also, knowing the required crystal
overtone frequency, ω

OT

2π×37.5MHz;

L++=

1

2

()

4

ω

5

2

L

= 5/[4(2π37.5×10E6)2(24+7+5)10E-12]

1

CCC

OSOUTEFF

= 2πfOT =

CCC

OSOUTEFFOT

Substituting values;

C

= 51.2pF – 1/(2π37.5E6)2×662.2E-9

2EFF

∴C

= 24pF 3

2EFF

Also, to confirm the frequency of

resonance, from equation 1;

f

= 1/[2π√{(51.2pF + 7pF + 5pF)662.2nH}]

r

∴ fr = 25.0MHz = 2fOT/3 3

So all the calculations look good. Using
preferred values, we can complete our design as
shown in Figure 2. (See Appendix A for a
detailed component list)

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 4 of 11

a

V

V

V

V

18

ADSP-218x DSP

ADSP-218x DSP

V

V

C

C

FB

FB

DDINT

DDINT

GND

GND

18

17

17

•

•

+2.5

+2.5

C

C

4

4

•

•

16

DDEXT

DDEXT

GND

GND

16

15

15

17

17

•

•

+3.3

+3.3

C

C

5

5

•

•

••

••

••

C

C

IN

GND

GND

12

12

IN

CLKIN XTAL

CLKIN XTAL

C

C

IS

IS

••

R

R

FB

FB

••

••

13 14

13 14

•

•

•

••

••

C

C

1

1

22pF

22pF

Y

Y

1

1

37.5MH z

37.5MH z

RD

RD

OT

OT

3

3

C

C

FBS

FBS

C

C

56pF

56pF

•

••

••

•

•

2

2

C

C

C

C

OUT

OUT

OS

OS

L

L

680nH

680nH

CLKOUT

CLKOUT

V

V

1

1

C

C

3

3

1nF

1nF

Figure 2: 37.5MHz, 3rd Overtone Crystal Oscillator

Test Results

A total of 15, 37.5MHz 3rd OT crystals
were tested from three different batches. A
second test of three different batches of five,
40MHz 3
same circuit component values as for the

37.5MHz crystals. Finally, a third test of three
34MHz 3
were performed on an ADSP-2189M EZ-KIT
LITE evaluation board. The results are tabulated
in Appendix B.

Note especially that all crystals are
oscillating within the ±50ppm (±1875Hz for

37.5MHz) frequency tolerance specified by the
crystal manufacturer. The worst-case deviation
is within 25ppm. The manufacturer’s test sheet
shows the average

37.5MHz by +29.8Hz. Checking the average for
our application shows the frequency to be high
by 292Hz. This error would normally be
considered insignificant and could be ignored.
The difference between the manufacturer’s

rd

OT crystals were tested using the

rd

OT crystals were tested. All tests

operating frequency is above

measured average frequency and our application
is 262Hz.

If it is desired to trim (reduce) the
operating frequency, we could increase the load
capacitance using the “Pullability Equation” to
estimate the additional load capacitance required.

This equation is given by …

ff

×=∆

2 )( +

∆

CC

L

1

Hz

2

CC

L

0

where

=

C

L

=

CC

10

eCapacitancLoadCrystal

ParameterseCapacitancCrystal,

Using the average crystal parameters
from Appendix C, the average pullability of the

37.5MHz crystals is ≈30Hz/pF. Hence by
increasing the load capacitance C

by

L

262Hz/30Hz/pF = 8.75pF, the mean frequency
should be close to the manufacturer’s quoted
measurements. No attempt was made to verify
this measurement as the operating frequency was

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 5 of 11

a

already well within the manufacturer’s
specifications for all parts.

A check of voltage at the input to the
crystal network shows the drive voltage to be
approximately 2.5Vpp or just under 1Vrms.
Lacking the instruments to measure crystal
current, a Spice simulation was run, using the
typical crystal parameters at the operating
frequency. This showed a current through R
(approximating the crystal ESR) of
approximately 1.2mA.

From the relation I
resistance is taken to be 65Ω, the crystal drive
power is estimated to be greater than 93µW,
which is considered sufficient to ensure
oscillation.

Startup times for several 37.5 and 40MHz
crystals were checked and ranged from a
minimum of ≈12ms up to a maximum of ≈35ms.

2

R1, where the crystal

1

Design Omissions

At this point it is useful to consider what
has been ignored. The most important design
considerations, ignored up till now, are the loop
gain and the crystal drive level. The design
process should aim for an overall loop gain (at
zero degrees) of at least +10dB. While an
amplifier gain of +30dB may seem sufficient, the
crystal feedback network (including the source
resistance of the amplifier) may have an
attenuation of more than +20dB, thus reducing
the gain margin. The loop gain is determined, in
part, by the internal amplifier and is not
something we have control over. We can
minimize losses in the external feedback network
by using high-Q RF capacitors and inductors and
keeping all lead lengths and PCB traces very
short. Using crystals with the lowest possible
equivalent series resistance (ESR) is also a good
idea.

The crystal drive level is usually
measured in microwatts (µW) and third overtone
crystals require a higher minimum

drive level

than fundamental mode crystals at the same
frequency. This is a parameter that is difficult to
measure and outside the scope of this paper.
While the manufacturer specifies the maximum
crystal drive level, typically 500µW to 1mW, the
minimum drive level is usually not mentioned.
This is unfortunate as it is one of the reasons why
some 3
Below a certain minimum drive level, a crystal
may not start, or will start and then stop
intermittently. The problem has been
exacerbated with the trend to lower operating
voltages for the amplifier. At V
available ac signal is about half the amplitude
obtained with a 5V supply. This reduces the
crystal drive to level to 25% of a 5V system.

The crystal drive level should be
measured and confirmed, if the facility is
available. If possible, crystals should be selected
with an ESR less than 50Ω. Extensive testing
for startup reliability should be done to ensure
operation for the limits of temperature, voltage
and production tolerances.

rd

OT crystal oscillators fail intermittently.

= 3.3V, the

DDEXT

Application Notes

At RF frequencies, care must be taken to
absolutely minimize trace and lead lengths.
Also, a ground plane is strongly recommended to
ensure stability and reduce EMI. All DSP power
pins should be bypassed to the ground plane with
10nF and/or 100nF surface mount capacitors,
right at the pins

Other oscillators on the same PCB should
be physically separated and carefully decoupled
to prevent mutual interaction via common power
supply impedances. Failure to do this can also
increase clock jitter.

The ground connections for capacitors
C

should be connected to the ground plane

1..5

with the shortest possible traces. The amplifier’s
ground pin(s) should be connected directly to the
ground plane via without a trace.

.

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 6 of 11

a

The actual frequency of oscillation
should be within the manufacturer’s specified
tolerance of the frequency marked on the crystal
package. This is usually quoted by the
manufacturer, in ppm. Typical tolerances are
±50 or ±100ppm. At 37.5MHz a tolerance of
±50ppm is ±1875Hz. If an accurate frequency
counter is available, this should be confirmed,
however, allowance should be made for the extra
load impedance of the counter probe, unless the
DSP has a buffered measurement point (e.g.
CLKOUT).

If the operating frequency were outside
this tolerance band it would indicate that the total
load capacitance is in error or there is some other
serious problem. Some crystal manufacturers
will quote a figure called the ‘pullability’ of the
crystal, usually in ppm/pF or Hz/pF. A typical
figure is about 30Hz/pF (see Appendix C,
parameter ‘P’). This shows that an error of a few
pF has only a small effect on the operating
frequency.

It was mentioned earlier that the two
external load capacitors, C

and C

1

2EFF

, are
normally equal values. It is possible to change
the ratio of these two capacitors while
maintaining the same total load capacitance.
This is sometimes done to increase or decrease

the feedback ratio and change the behavior of the
oscillator. The objective might be to increase
start-up speed with a low gain amplifier or
improve stability if the amplifier gain is too high.
These are not common requirements and are
beyond the scope of this paper.

5th and Higher Overtone Crystals

The same principles described in this note
apply to using 5
crystals. The parallel circuit consisting of C
and the stray output capacitance should be
chosen to resonate halfway between the chosen
overtone frequency and the next lowest overtone.

For a 5
the 5

th

OT crystal, this would require fR ≈ ⅘ of

th

OT frequency, fOT.

It is still necessary to provide the
manufacturer’s specified load capacitance across
the crystal and provide the correct network phase
and gain conditions to initiate and support
oscillation only at the chosen overtone. Note
that the circuit becomes more critical of
component tolerances as the overtone order
increases, and 5th order operation, and higher, is
not recommended for production applications.
For clock frequencies up to 75MHz, it should not
be necessary to use 5

th

overtone and higher-order

2

th

OT mode crystals.

, L1

Appendix A

Components for the Example 37.5MHz 3

Ref

Designato

r

C1 22pF, ±5%, 50V, NP0 SMD 0603 Panasonic ECJ-1VC1H220J

C2 56pF, ±5%, 50V, NP0 SMD 0603 Panasonic ECJ-1VC1H560J

C3 1nF, ±5%, 50V, NP0 SMD 0603 Panasonic ECJ-1VC1H102J

L1 680nH, ±10%, Q

Y1 37.5MHz, 3rdOT Crystal Cardinal

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 7 of 11

Description Package

=40, DCR<0.26Ω, SRF

min

=175MHz SMD 1008 API Delevan 1008-681K

min

rd

Overtone Test Circuit

Manufacture

r

Part Number

CSM1-A1B2C2-

100-37.5D18-3

Appendix B: 3rd OT Crystal Test Results

y

q

(

)

)

(

(

(

g

y

q

(

)

)

(

(

(

g

q

(/2)

(

ADSP-2189M EZ-KIT. 3rd OT Crystal Oscillator Frequency Measurements

Tests on a selection of 3rd OT Crystals
Frequency Counter: HP Model 5328A
Approx 2min allowed for oscillator frequenc

FL = 37.50000 MHz Tolerance 50ppm 1875 Hz
CL = 18 pF

FL
Xtal ppm Hz CLKOUT
CLP 1 -5.1 -191.3 75000.62 37500.31 310.0

ThruHole) 2 4.8 180.0 75001.24 37500.62 620.0
3 -3.54 -132.8 75000.67 37500.34 335.0
4 4.23 158.6 75001.14 37500.57 570.0
5 -3.19 -119.6 75001.08 37500.54 540.0
CSM1 6 11.31 424.1 75001.08 37500.54 540.0

SMD) 7 9.46 354.8 75000.47 37500.24 235.0
8 3.03 113.6 75000.32 37500.16 160.0
9 4.23 158.6 75000.35 37500.18 175.0
10 9.5 356.3 75001.02 37500.51 510.0
CX5 1 -6.91 -259.1 75000.03 37500.02 15.0

SMD) 2 -3.72 -139.5 75000.19 37500.10 95.0
3 -4.19 -157.1 75000.18 37500.09 90.0
4 -4.33 -162.4 75000.15 37500.08 75.0
5 -3.66 -137.3 75000.22 37500.11 110.0

0.79 29.8 75000.58 37500.29 292.0

Av

to stabilize (typically drifts up about 200Hz)

Measured Fre

kHz

uency

Xtal(kHz

a

Error-Hz

FL = 40.00000 MHz Tolerance 50ppm 2000 Hz
CL = 18 pF

NOTE: Same 3rd OT LC circuit values as used for 37.5MHz circuit.

stal frequency over clocks the 2189M DSP and is not recommended

This cr
FL
Xtal ppm Hz CLKOUT
CLP 11 6.72 268.8 80000.91 40000.46 455.0

ThruHole) 12 10.72 428.8 80000.69 40000.35 345.0
13 7.35 294.0 80001.40 40000.70 700.0
14 -0.67 -26.8 80000.73 40000.37 365.0
15 5.39 215.6 80000.34 40000.17 170.0
CSM1 16 0.72 28.8 80000.98 40000.49 490.0

SMD) 17 9.68 387.2 80000.36 40000.18 180.0
18 2.05 82.0 80000.44 40000.22 220.0
19 -0.17 -6.8 80000.34 40000.17 170.0
20 1.72 68.8 80000.47 40000.24 235.0
CX5 1 -4.12 -16.5 80000.12 40000.06 60.0

SMD) 2 -5.06 -20.2 79999.98 39999.99 -10.0
3 -4.12 -16.5 80000.07 40000.04 35.0
4 -7.36 -29.4 79999.80 39999.90 -100.0
5 -9.41 -37.6 79999.22 39999.61 -390.0

0.896 108.0 80000.39 40000.20 195.0

Av

FL = 34.0000 MHz Tolerance 50ppm 1700 Hz
CL = 20 pF

NOTE: Same 3rd OT LC circuit values as used for 37.5MHz circuit.
FL
Xtal ppm Hz CLKOUT Xtal
CLP 21 6.72 228.5 68000.21 34000.11 105.0

ThruHole) 22 10.72 364.5 67999.68 33999.84 -160.0
23 7.35 249.9 68002.05 34001.03 1025.0

-0.67 -22.8

5.39 183.3

Measured Fre

kHz

Measured Fre

uency (Hz)

Xtal(kHz

uency (Hz)

Error-Hz

Error-Hz

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 8 of 11

Appendix C: Manufacturer’s Sample Crystal Parameters

a

Ref Freq 37.50000 MHz (3rd OT)

CL = 18 pF

Xtal ppm Hz ppm/pF Ohm ppm Hz pF fF mH Hz/pF
CLP 1 9.50 356.3 0.7 83.9 -5.10 -191.3 1.883 0.583 30.9 27.7
(ThruHole) 2 4.23 158.6 0.7 77.5 -10.13 -379.9 1.847 0.572 31.5 27.2
3 3.03 113.6 0.7 81.3 -11.44 -429.0 1.871 0.581 31.0 27.6
4 11.31 424.1 0.9 84.5 -5.70 -213.8 1.862 0.676 26.6 32.1
5 9.46 354.8 0.9 75.6 -8.99 -337.1 1.880 0.738 24.4 35.0
CSM1 1 4.23 158.6 0.9 72.8 -13.57 -508.9 1.902 0.714 25.2 33.8
(SMD) 2 -5.10 -191.3 0.8 64.2 -24.25 -909.4 2.037 0.653 27.6 30.5
3 4.80 180.0 0.8 85.0 -10.91 -409.1 1.897 0.624 28.9 29.6
4 -3.19 -119.6 0.9 60.8 -20.64 -774.0 2.027 0.698 25.8 32.6
5 -3.54 -132.8 0.9 57.4 -21.64 -811.5 2.271 0.733 24.6 33.4
CX5 1 -6.91 -259.1 0.7 49.9 -20.91 -784.1 1.652 0.553 32.6 26.8
(SMD) 2 -4.19 -157.1 0.8 42.8 -19.05 -714.4 1.574 0.587 30.7 28.7
3 -3.72 -139.5 0.7 50.9 -18.24 -684.0 1.644 0.574 31.4 27.9
4 -4.33 -162.4 0.8 46.7 -19.06 -714.8 1.676 0.584 30.8 28.3
5 -3.66 -137.3 0.8 47.1 -18.55 -695.6 1.427 0.584 30.8 29.0
AVG 0.79 29.8 0.80 65.36 -15.21 -570.5 1.830 0.630 28.9 30.0

Ref Freq 40.00000 MHz (3rd OT)

CL = 18 pF

Xtal ppm Hz ppm/pF Ohm ppm pF fF mH Hz/pF
CLP 1 6.72 268.8 0.9 40.8 -10.74 -429.6 2.060 0.710 22.3 35.3
(ThruHole) 2 10.72 428.8 1.0 33.6 -8.72 -348.8 2.051 0.788 20.1 39.2
3 7.35 294.0 0.8 42.4 -9.21 -368.4 2.080 0.668 23.7 33.1
4 -0.67 -26.8 0.9 36.6 -18.40 -736.0 2.042 0.718 22.0 35.7
5 5.39 215.6 1.0 33.0 -13.62 -544.8 1.739 0.761 20.8 39.1
CSM1 1 0.72 28.8 0.8 37.9 -16.45 -658.0 2.851 0.725 21.8 33.4
(SMD) 2 9.68 387.2 0.8 47.4 -6.79 -271.6 2.817 0.691 22.9 31.9
3 2.05 82.0 0.8 42.5 -14.71 -588.4 2.826 0.699 22.6 32.2
4 -0.17 -6.8 0.9 34.0 -18.38 -735.2 2.824 0.764 20.7 35.2
5 1.72 68.8 0.8 37.3 -15.20 -608.0 2.827 0.712 22.2 32.8
CX5 1 -4.12 -164.8 0.8 58.0 -20.09 -803.6 1.562 0.627 25.2 32.8
(SMD) 2 -5.06 -202.4 0.8 61.2 -20.82 -832.8 1.694 0.623 25.4 32.1
3 -4.12 -164.8 0.8 57.7 -19.82 -792.8 1.679 0.620 25.5 32.0
4 -7.36 -294.4 0.8 54.8 -23.63 -945.2 1.478 0.636 24.9 33.5
5 -9.41 -376.4 0.8 58.3 -25.45 -1018.0 1.466 0.625 25.3 33.0
AVG 0.90 35.8 0.85 45.03 -16.14 -645.4 2.133 0.691 23.0 34.1

FL Ts Rs Fs C0 C1 L1 P

FL Ts Rs Fs C0 C1 L1 P

Ref Freq 34.00000 MHz (3rd OT)

CL = 20 pF

Xtal ppm Hz ppm/pF Ohm ppm Hz pF fF k Hz/pF
CLP 1 -12.40 -421.6 26.2 2.900 1.200 149 38.9
(ThruHole) 2 -13.30 -452.2 26.7 3.000 1.180 148 37.9
HC49/LP 3 -20.80 -707.2 26.6 3.000 1.170 151 37.6
4 13.60 462.4 31.0 3.000 1.140 133 36.6
5 11.20 380.8 28.6 3.000 1.250 130 40.2
AVG -4.34 -147.56 27.82 2.980 1.188 142 38.2

FL Ts Rs Fs C0 C1 Q P

EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 9 of 11

a

Acknowledgements

Special thanks to Dave Babcock and Maralyn Thomas of Cardinal Components, for providing a

rd

variety of 3
my colleagues Steven Cox, David Katz, Greg Koker and Glen Ouellette for suggestions and proof
reading. Regrettably the author must assume responsibility for any remaining errors.

References

OT crystals, test parameters, application advice and proof reading this note. Thanks also to

Cardinal Components, Inc
Wayne Interchange Plaza II
155 Route 46 West
Wayne, NJ 07470

Tel: [phone]

http://cardinalxtal.com/cardinal/index.html

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a

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EE-168: Using Third Overtone Crystals with the ADSP-218x DSP Page 11 of 11