Direct frequency modulation of an ADPLL for bluetooth/GSM with injection pulling elimination

Abstract

We propose and demonstrate a Gaussian frequencyshift keying and Gaussian minimum-shift keying (GMSK) pulseshape filtering for wireless RF transmitters with an arbitrary reference frequency. The filter is software controlled to work in a multistandard radio. Spurs, which are due to the frequency injection pulling, in cases when the reference harmonics are close enough to the oscillating frequency, are avoided by means of retiming the reference clock by the RF oscillator. Baseband clock for the pulse-shape filtering is derived through a simple fractional-N division of the reference frequency. This saves area and power since it is no longer required to create a low-jitter clock for baseband symbol generation and modulating data. It is especially advantageous when the available reference frequency is not an integer multiple of the symbol rate. The presented transmitter is realized without any explicit analog filtering and is part of a commercial single-chip fully compliant Bluetooth radio fabricated in a digital 130-nm CMOS process. We demonstrate the software programming capability through an experimental GMSK modulation for the global system for mobile communication.Index Terms-Bluetooth, frequency synthesizers, Gaussian frequency-shift keying (GFSK), Gaussian minimum-shift keying (GMSK), global system for mobile communication (GSM), interpolation, injection pulling, pulse-shaping filter, retiming, software defined radio, transmitter.

Analysis and Improvement of Direct-Conversion Transmitter Pulling Effects in Constant Envelope Modulation Systems

“…In (4), is equivalent to and is regarded as an equivalent injection-induced source to cause frequency modulation in a PLL. Integrating (4) yields the resulting LO output phase as (6) where represents an initial oscillation phase. Notably, the above equation interprets the resulting LO output phase as a combination of the phase-locking mechanism and the injectionlocking process [20].…”

“…The instantaneous phase modulation of the PM signal can be extracted by using the vector signal analyzer (VSA). Therefore, we can develop a corresponding frequency-domain model for phase noise analysis of a directly modulated self-injection PLL by taking the Laplace transforms of (2), (6), and (7), as shown in Fig. 4.…”

Precise Delay Alignment Between Amplitude and Phase/Frequency Modulation Paths in a Digital Polar Transmitter

“…The CKR edge time stamps are now synchronous to the RF oscillator, in which time separation between the closest CKR and CKV edges is time invariant. In this embodiment, it is beneficial for avoiding injection pulling, in which the slowly varying timing separation between CKR and CKV causes the oscillator to be pulled, thus creating frequency-beating events that are exhibited as spurs in the output generated [14]. Fig.…”

“…Being synchronous to the CKV clock, the pulse-shaping filter clock rate is now channel dependent. This necessitates adjustment of the coefficient or operating in an interpolative manner, as described in [14] and Chapter 5 of [16]. 7.…”

Fine and wide frequency tuning digital controlled oscillators utilizing capacitance position sensitivity in distributed resonators

“…Aside from its advantages of having less process, voltage and temperature (PVT) dependence it also allows such techniques as direct frequency modulation [1,2], and allows ease of implementation of fast settling techniques such as dynamic filter bandwidth control [3], and direct reference feed-forwarding method [4,5].…”