OPTIMIZED DIFFERENTIAL GFSK DEMODULATOR

PRESENTED BY V.HARINATHREDDY (13S15A0401)

INTRODUCTION• Gaussian frequency shift keying (GFSK) is a promising

digital modulation scheme. • The design of simple and high-performance receivers

we develop an optimized differential GFSK demodulator and investigate the phase wrapping issue in its implementation.

• In GFSK Bit-Error-Rate(BER) performance improvement in comparison with conventional differential demodulators in both AWGN and flat fading channels.

BLOCK DIAGRAM

LNA DESIGNThe received signal is first passed through a receiver

filter with transfer function H(f), then the phase differential detection is performed on the output signal of the filter by the LNA block.

LNA was designed with 50 Ohm input impedance to provide the termination for preceding external components.

And also LNA was designed with high Gain, low Noise, Sufficient Linearity and Low Power consumption.

MIXER DESIGN

Low noise design is still important since Mixer is one of the front End Block. Mixer required Linearity is higher than that of LNA.

Two types of Mixers are available in GFSK demodulator they are Passive Mixer and Active Mixer.

Passive mixers provide lower power consumption and active mixers provide conservation Gain to LNA block.

VCO DESIGN

• VCO must be able to cover the entire band and some more to compensate process variation.

• Tuning sensitivity must be high enough to cover the range but low enough to reduce noise due to control signal.

• Phase noise requirement came from third and higher interference specification

COMPLEX FILTER DESIGN

• Complex filter preferred Butterworth 6th order filter because it provide good group delay response and same magnitude for all poles.

• Large channel lengths(6 um) are used to minimize flicker noise, improve matching, linearity, and avoid using cascade transistors.

• A simple input gain stage(15dB) is used to minimize the input referred noise

LIMITER AND RSSI

 low-voltage low-power limiter, RSSI, and demodulator designs for a low-IF wireless GFSK receiver. 

 The circuits in limiter and RSSI are all pseudo differential to minimize the requirement of the voltage headroom.

The GFSK demodulator is implemented by a delay-locked loop associated with the techniques of digital offset cancellation and modified phase-frequency detection. 

DIGITAL DEMODULATOR• This may provide some gain in the signal-to-noise

ratio (SNR). In the case of Gaussian noise, the gain in SNR leads to improvement in BER. To facilitate the design of an optimum differential demodulator.

• For the simplification of analysis, we will first consider the AWGN channel. The result can then be easily extended to flat fading channels.

DC OFFSET CANCELLATIONBit decision obtain the bit stream based on the output of

the demodulator.Track and compensate the DC offset caused by the low

frequency offset between receiver and transmitter and frequency drifting.

During preamble and trailer are integrate the signal to get estimation of the DC offset.

After that a low pass filter to track the DC changing in the coming signal

EXISTING TECHNIQUESThe LDI receiver is low-cost and easy to implement, but

it suffers from a relatively poor power efficiency compared to more sophisticated receivers.

Lee proposed a zero-intermediate frequency zero-crossing demodulator (ZIFZCD). The performance of this demodulator is not as good as the LDI detector.

Lampe et.al. proposed a noncoherent sequence detector. This receiver can achieve significant performance gain of more than 4 dB over the discriminator-based detector. Dis advantage is complexity required for a two-state trellis search.

DIF. GFSK DEMODULATION

A simple demodulator for GFSK receivers, which averages the phase based on the signal to noise ratio (SNR) maximizing criterion, and does not require knowledge of the exact modulation index. Compared to demodulators with similar complexity, such as the LDI, GFSK receiver can achieve superior performance.

The Bit Error Rate (BER) performance improvement is not a strictly increasing function of the modulation index .ℎ

PHASE WRAPPING PROBLEM

When realizing these phase differential demodulation algorithms, however, there is an implementation problem. Recall that our differential operations are performed on the phase function ( ). ( ) is not only 𝜙𝑡 𝜙 𝑡noisy, but also suffers from the phase wrapping problem since it assumes a finite range of 2 Pi.

To solve this problem in GFSK the received signal ( ) 𝑟 𝑡is multiplied by a -delayed and /2 phase-shifted 𝑇 𝜋version of itself and then sampled at the symbol rate to give the decision statistic.

BER performance in AWGN channels.

CONCLUSION

GFSK modulated systems including Bluetooth. Performance of this demodulator has been studied by theoretical analysis and simulations. It has been shown that the optimized demodulator can achieve evident improvements over the conventional demodulators and provide a favorable performance in both AWGN and flat fading channels.

THANK YOU