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INSPECTION, MEASUREMENT, AND TEST

INSPECTION, MEASUREMENT, AND TEST 19.29

and noise elements in the spectrum. Some common parameters that are results of this test include—
total harmonic distortion (THD), signal-to-noise ratio (SNR) and signal-to-noise + distortion ratio
(SNDR). All these are indicative of the performance of the device.

19.2.8 Testing RF Devices
Market Segments. The types of devices that will be included in this consumer market segment are at
a high integration level and include RF reception or transmission, or both. This includes devices that
go into cellular telephones, TV tuners, WLAN Internet, Bluetooth, and Ultra Wide Band applications.
Definition of an RF Device. The term RF refers to an analog signal, called a carrier, typically
above 100MHz, that is modulated to contain information. This signal is propagated through the air-
ways and then the carrier signal is removed and the modulated data are decoded. There are many
devices manufactured today which can be considered RF devices. RF techniques are used in both the
wireless and wired, or wireline industries. The wireless RF industry comprises cellular phones, wire-
less LAN or WLAN, Bluetooth, Ultra Wide Band, and other standards of sending information from
point a to point b without wires. In contrast, the wireline RF industry comprises cable TV tuners and
other appliances used to send information through cables.
Building Blocks of RF. There are all kinds of devices that use RF signals, but a “pure” RF device
is one that has only RF in, RF out, and a power supply. This kind of device requires a traditional RF
test approach and therefore a specific type of test system that has sufficient RF source and measure
capabilities to meet the device specification. As devices evolve, more and more functionality is being
placed on a single substrate, thus the emergence of RF SOC devices. RF SOC devices have RF in, RF
out along with digital and analog controls. These kinds of devices will have functions such as regis-
ters, digital interfaces, memories, mixed-signal blocks, as well as RF inputs and outputs. This kind of
device requires a much more flexible test system that can handle the variety of signal types mentioned.
All RF tests start with understanding the basic building blocks of RF SOCs. These basic build-
ing blocks are amplifiers that take an input signal and increase its power, mixers that take an input
signal and translate it from one frequency into another, filters that take an input spectrum and mod-
ify certain frequency components, and voltage controlled oscillators (VCOs) that convert a voltage
into a frequency.

System-Level Tests. System-level tests, for example, testing the IC as a radio rather than a series
of blocks, provides true performance verification since the device is tested under conditions similar
to its end-use environment. Examples of these types of measurements include adjacent channel
power (ACPR), error vector magnitude (EVM), and bit error rate (BER).
Bit error rate. BER is the number of error bits divided by the number of transmitted bits. The
bit sequence to be sent to the DUT is coded into an RF modulated signal. The DUT then demodu-
lates the signal to the in-phase and quadrature (I and Q) signals. The I and Q signals are decoded to
get the digital data (bit sequence) that were originally sent to the DUT. The digital data from the
DUT are then compared to the original bit sequence to determine the BER.
Error vector magnitude. EVM is a measure of modulation or demodulation accuracy. The ideal
modulation vector is compared to the resulting vector coming from the DUT. Error vector magnitude
is the root mean square value of the error vector over time at the instant of the symbol clock transitions.

EVM = rms error vector ×100%
outermost most magnitude
Or, expressed in decibels:

×
EVM = 20 log EVM% dB
100%

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