OPTIMIZED DIFFERENTIAL GFSK DEMODULATOR

1. OPTIMIZED DIFFERENTIAL GFSK
DEMODULATOR
PRESENTED BY
V.HARINATHREDDY (13S15A0401)

2. 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.

3. BLOCK DIAGRAM

4. LNA DESIGN
 The 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.

5. 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.

6. 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

7. 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

8. 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.

9. 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.

10. DC OFFSET CANCELLATION
 Bit 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

11. EXISTING TECHNIQUES
 The 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.

12. 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.

13. 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 𝜙(𝑡). 𝜙(𝑡) is not only
noisy, 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(𝑡)
is multiplied by a 𝑇 -delayed and 𝜋/2 phase-shifted
version of itself and then sampled at the symbol rate to
give the decision statistic.

14. BER performance in AWGN channels.

15. 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.

16. THANK YOU