The document outlines frequently asked questions regarding frequency products, particularly crystals and oscillators, detailing essential specifications needed for ordering, the piezoelectric effect, and performance characteristics across various temperature ranges. It discusses types of crystals like fundamental and overtone, along with comparisons between different oscillator types (SPXO, VCXO, TCXO, OCXO) based on their stability and application. Additionally, it provides information about product availability, package sizes, and where to find more technical assistance.

1. Frequently Asked Questions
About Frequency Products

2. What is the minimum information
needed to order a crystal?
2
 We need the answers to the following
questions:
 Frequency in kHz or MHz – preferably to six
decimal places, anything after the significant
digits will be taken as zero unless indicated.
 Holder style
 Adjustment (sometimes called Calibration)
tolerance (in ppm)
 Temperature stability over operating
temperature range (in ppm)
 Operating temperature range in degrees
centigrade
 Load capacitance either parallel resonant in pF
or series resonant (SR)

3. What is load capacitance?
3
 This is the capacitance of the oscillator
circuit as presented to the quartz crystal
resonator.
 The most common type of crystal is
parallel resonant where the crystal
operates at a frequency above its series
resonant frequency (point of lowest
impedance).

4. What is the Piezoelectric effect?
4
 Quartz crystals depend upon the
piezoelectric effect in order to function.
 It’s based upon a quartz resonator
coated with an electrode on both faces
then mounted in a sealed holder.
 Application of an external AC voltage to
these electrodes gives rise to a
mechanical vibration.

5. Will the crystal operate outside its
specified temperature range?
5
 Yes!
 If for example a crystal is specified over
–10 to +60°C it will perform without any
issue over –40 to +85°C but it is possible
that it will fall outside its specified stability.
 This may not matter if the application
needs just a stable frequency rather than
an accurate frequency.

6. Why is it important to specify the
operating temperature range?
6
 See slide 5.
 Also if the temperature goes significantly
outside the specified temperature range it
is possible that damage to the crystal may
be caused.

7. Explain the differences between
fundamental crystals and overtone
crystals
7
 A fundamental crystal oscillates at the
frequency determined by the dimensions
of the quartz blank.
 Overtone crystals operate at either the
3rd, 5th or 7th multiple of the
fundamental.
 The crystal is specially designed to operate
in these modes.

8. Where do I find IQD product
specifications?
8
 Specifications can be found on our website
www.iqdfrequencyproducts.com
 If you require further information please
contact one of our Sales offices.

9. Who do I contact at IQD for
technical assistance?
9
 Either call one of our Sales offices and ask
for Applications Support.
 Or contact our Applications Support
department direct via email.

10. Thinking of changing an existing
design from using thru-hole
crystals to SMD crystals – what do I
need to consider?
10
 This depends upon the application. If for
example the crystal is pullable i.e. the
frequency can be changed by varying the
load capacitance of the crystal by electrical
means, then this may be difficult to
achieve. For example strip blank SMD
crystals have a much lower pullability than
the HC49 style round blank package.
 This exercise should not be undertaken
lightly, please feel free to contact our
Applications Support department for
further advice.

11. Is it preferable to design-in a crystal
or an oscillator for my application?
11
 This depends upon the application. If you
are designing a discrete circuit and have
little or no experience of oscillator design
then it may be preferable to use a
packaged oscillator since this will remove
any tolerance issues.
 It’s "easy" to design a "one off" for lab use
but if you have to manufacture large
numbers in volume this may give rise to all
sorts of issues.
 If you are using a chipset which requires a
crystal to drive it then this decision is much
simpler since the on board oscillator circuit
should have been optimised.

12. What are the differences between
SPXO's/ VCXO's / TCXO's and
OCXO's
12
 SPXO (or Clock Oscillator)
 The basic type of oscillator and consists of a
crystal and a basic drive circuit. Since there is no
form of compensation the frequency/
temperature stability is essentially that of the
crystal itself – typically ±50ppm.
 VCXO (Voltage Controlled Crystal Oscillator)
 An oscillator which relies on the inherent
pullability of the quartz crystal in order to allow
the output frequency of the oscillator output to
be changed by application of an external voltage.
This change is limited to a few tens of ppm,
typically ±100ppm. As with SPXO's the
frequency/temperature stability is that of the
crystal itself.

13. 13
 TCXO (Temperature Compensated Crystal
Oscillator)
 Where the stability of the crystal is not sufficient
it may be necessary to use a TCXO. This type of
device is used where the stability of a basic
quartz crystal is insufficient. Typically TCXO's can
achieve a stability of less than 1ppm as opposed
to a typical crystal of 30ppm.
 OCXO (Oven Controlled Crystal Oscillator)
 The "ultimate" piezoelectric product is the
OCXO. Where a high stability is required then
this type of product should be considered. These
types of devices offer performances of typically
3E10-9.

14. Are products still available that
were previously in the Data Book
or on the website but do not
appear currently?
14
 Often this is the case but not in all
situations.
 If a product has become obsolete then
please discuss with Applications Support;
in most cases a suitable alternative product
can be offered.

15. Does IQD offer a quick turnaround
on oscillators?
15
 Yes.
 If the device that you are looking for is not
a stock part then in some cases a
programmable version may be available.
These are compatible with the fixed
frequency device and can often be
supplied in a few working days – custom
fixed frequency may take at least 6 weeks
to produce.
 Programmable oscillators particularly lend
themselves to prototyping where time is
critical.

16. Are IQD's products available
through Distribution?
16
 In most cases, yes.
 Please look on our website to see a list of
our Distributors and Reps.

17. Does IQD offer products which are
not on its website or in the Data
Book?
17
 Yes
 Our Engineering department is constantly
developing our product range and indeed
much of its capability is in customisation.
 In any event please contact us!

18. Why are crystal packages getting
smaller?
18
 This situation is being driven by the
electronics industry in general and the
need for more portability in particular.
 There is a downside to this however which
is that the smaller the crystal blank the
higher the starting frequency.

19. What are the most cost effective
crystal and oscillator packages to
consider for new designs?
19
 For quartz crystals the HC49/4HSMX and
for oscillators (SPXO's) the CFPS-72/CFPS-
73.
 Please contact one of our Sales offices for
more information.

20. Can I obtain the test results for my
products?
20
 Samples are automatically despatched
with the appropriate test results.
 Production quantities are tested to the
appropriate AQL level and the results
retained within our company records.
 For further information please contact us.

21. What is the most common cut of
quartz crystal?
21
 AT cut quartz accounts for the majority of
crystals produced in the 1 to 200MHz
range.
 This refers to the nominal angle with
respect to the Z axis of the quartz bar.
 The angle of cut determines the
frequency/ temperature performance and
is usually selected by the crystal
manufacturer.

22. Standing out from the crowd
22