Frequently Asked QuestionsAbout Frequency Products

What is the minimum information needed to order a crystal

2

We need the answers to the following

questions

Frequency in kHz or MHz ndash 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)

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)

What is the Piezoelectric effect

4

Quartz crystals depend upon the

piezoelectric effect in order to function

Itrsquos 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

What is the minimum information needed to order a crystal

2

We need the answers to the following

questions

Frequency in kHz or MHz ndash 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)

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)

What is the Piezoelectric effect

4

Quartz crystals depend upon the

piezoelectric effect in order to function

Itrsquos 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

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)

What is the Piezoelectric effect

4

Quartz crystals depend upon the

piezoelectric effect in order to function

Itrsquos 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

What is the Piezoelectric effect

4

Quartz crystals depend upon the

piezoelectric effect in order to function

Itrsquos 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

Will the crystal operate outside its specified temperature range

5

Yes

If for example a crystal is specified over

ndash10 to +60degC it will perform without any

issue over ndash40 to +85degC 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

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

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

Where do I find IQD product specifications

8

Specifications can be found on our website

wwwiqdfrequencyproductscom

If you require further information please

contact one of our Sales offices

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

Where do I find IQD product specifications

8

Specifications can be found on our website

wwwiqdfrequencyproductscom

If you require further information please

contact one of our Sales offices

Where do I find IQD product specifications

8

Specifications can be found on our website

wwwiqdfrequencyproductscom

If you require further information please

contact one of our Sales offices

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

Thinking of changing an existing design from using thru-hole crystals to SMD crystals ndash what do I need to consider

10

This depends upon the application If for

example the crystal is pullable ie 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

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

Itrsquos 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

What are the differences between SPXOs VCXOs TCXOs and OCXOs

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 ndash typically plusmn50ppm

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 plusmn100ppm As with SPXOs the frequencytemperature stability is that of the crystal itself

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 TCXOs 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

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

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 ndash custom

fixed frequency may take at least 6 weeks

to produce

Programmable oscillators particularly lend

themselves to prototyping where time is

critical

Are IQDs products available through Distribution

16

In most cases yes

Please look on our website to see a list of

our Distributors and Reps

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

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

What are the most cost effective crystal and oscillator packages to consider for new designs

19

For quartz crystals the HC494HSMX and

for oscillators (SPXOs) the CFPS-72CFPS-

73

Please contact one of our Sales offices for

more information

What are the most cost effective crystal and oscillator packages to consider for new designs

19

For quartz crystals the HC494HSMX and

for oscillators (SPXOs) the CFPS-72CFPS-

73

Please contact one of our Sales offices for

more information

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

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

Standing out from the crowd

22

Standing out from the crowd

22