RF2512 データシートの表示（PDF） - RF Micro Devices

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RF2512

UHF TRANSMITTER

RF Micro Devices 

RF2512

With these known, it is then possible to determine the

values of the filter components.

C1

=

τ---1-

τ2

⋅

K-----P---D-----⋅---K----V---C----O--

ω2LBW ⋅ N

⋅

1-----+-----(--ω-----L---B---W-----⋅---τ---2---)--2-

1 + (ωLBW ⋅ τ1)2

C2

=

C1

⋅

æ

è

τ---2-

τ1

–

1øö

R2

=

-τ---2--

C2

As an example, consider a loop bandwidth of 50kHz, a

phase margin of 45°, a divide ratio of 64, a KVCO of

20MHz/V, and a KPD of 0.01592mA/2πrad. Time con-

stant τ1 is 1.31848µs, time constant τ2 is 7.68468µs,

C1 is 131.15pF, C2 is 633.26pF, and R2 is 12.14kΩ.

In order to perform these calculations, one will need to

know the value of two constants, KVCO and KPD. KPD is

calculated by dividing the charge pump current by 2π.

For the RF2512, the charge pump current is 40µA.

KVCO is best found empirically as it will change with

frequency and board parasitics. By briefly connecting

pin 23 (LOOP FLT) to VCC and then to ground, the fre-

quency tuning range of the VCO can be seen. Dividing

the difference between these two frequencies by the

11 difference in the voltage gives KVCO in MHz/V.

The control lines provide an interface for connecting

the device to a microcontroller or other signal generat-

ing mechanism. The designer can treat pin 16 (MOD

IN), pin 15 (DIV CTRL), pin 14 (MOD CTRL) and pin 7

(LVL ADJ) as control pins whose voltage level can be

set.

General RF bypassing techniques must be observed

to get the best performance. Choose capacitors such

that they are series resonant near the frequency of

operation.

Board layout is always an area in which great care

must be taken. The board material and thickness are

used in calculating the RF line widths. The use of vias

for connection to the ground plane allows one to con-

nect to ground as close as possible to ground pins.

When laying out the traces around the VCO, it is desir-

able to keep the parasitics equal between the two legs.

This will allow equal valued inductors to be used.

11-18

Pre-compliance testing should be performed during

the design process. This can be done with a GTEM cell

or at a compliance testing laboratory. It is recom-

mended that pre-compliance testing be performed so

that there are no surprises during final compliance

testing. This will help keep the product development

and release on schedule.

Working with a laboratory offers the benefit of years of

compliance testing experience and familiarity with the

regulatory issues. Also, the laboratory can often pro-

vide feedback that will help the designer make the

product compliant.

On the other hand, having a GTEM cell or an open air

test site locally offers the designer the ability to rapidly

determine whether or not design changes impact the

product's compliance. Set-up of an open air test site

and the associated calibration is not trivial. An alterna-

tive is to use a GTEM test cell.

After the design has been completed and passes com-

pliance testing, application will need to be made with

the respective regulatory bodies for the geographic

region in which the product will be operated to obtain

final certifications.

Conclusions

The RF2512 is an FM/FSK UHF transmitter that fea-

tures a phase-locked output. This device is suitable for

use in a CFR Part 15.231 compliant product as well as

a local oscillator signal source. Further, the RF2512 is

packaged in a low cost SSOP-24 plastic package and

requires few external parts, thus making it suitable for

low cost designs.

Rev B9 010509

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