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Bluetooth Transceiver IC Test
Nov 15, 2017

Bluetooth technology consists of four main components: application  software, Bluetooth stack, hardware and antenna. This article focuses on  hardware and RF front-end transceivers, highlighting various test  parameters defined in the Bluetooth specification.

Bluetooth Transceiver

Bluetooth Transmitter---The Bluetooth  wireless signal is modulated by Gaussian frequency shift keying (GFSK).  The transmitted data (Tx) is filtered by a Gaussian filter, and then the  VCO frequency is modulated by the output of the filter. Depending  on the logic level of the serial input data stream, the VCO frequency  will deviate from its center frequency to both positive and negative  terminals. The offset determines the modulation index of the  transmitter. The modulated signal is amplified and transmitted by the  antenna.
Bluetooth wireless signals operate in  half-duplex mode, with an RF multiplex switch (in front of the antenna)  to connect the antenna to transmit or receive mode.

Bluetooth Receiver---Similar to the device receiving part, GFSK signals transmitted from another Bluetooth device are also received by the antenna. During this period, the switch is connected to a low-noise amplifier (LNA) to amplify the received signal (Rx). The  next mixer downconverts the received signal to an IF frequency  (typically a few MHz), and the PLL / VCO part used for transmission  during this step acts as a receiver downconverting local oscillator and  demodulates the IF signal, even recover the data.

Spread Spectrum

One of the unique features of Bluetooth wireless communication is that it uses spread spectrum technology.

The two main  types of spread spectrum are Frequency Hopping (FHSS) and Direct  Sequence (DSSS), which are used when the original data is modulated on  the carrier and transmitted using the same frequency range as the  end-of-line frequency hopping code FHSS system. In  this way, the data lost due to a certain frequency interference can be  transmitted through another frequency. The extended code generator in  the FHSS directly modulates the carrier frequency by the GFSK modulation  technique.

GFSK Modulation

GFSK is a modulation technique that linearly modifies a portion of the carrier frequency of a carrier cycle by a data for a duration of one bit. The frequency-conversion rate is a function of the data rate, and the magnitude of the frequency-shift is a function of the data amplitude. The correlation between them Modulation index β to represent.

Bluetooth Transceiver Test Specification

The PLL / VCO  encodes on the Bluetooth channel (2.4 ~ 2.5GHz) using the required  digital mode. Once the device has completed the channel encoding, it  will have a predetermined wait time to set the VCO to the encoded  carrier frequency.

Then placed the PLL in the open loop so that it can be modulated and provide  pseudo-random bit sequence (PRBS) data to the Tx data pins. An RF port is used to connect the RF receiver to the Bluetooth transmitter  antenna. After a predefined period of time in the digital mode, the RF receiver is triggered to begin receiving the transmitted signal and  perform a Fast Fourier Transform on the digital samples received by the  microwave receiver . For the captured signal,  the power of the carrier frequency and frequency part is searched on  both sides of the GFSK signal, that is, 20 dB is subtracted from the  encoded carrier frequency, and then the bandwidth is calculated.

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