Generation of RF pulsewidth modulated microwave signals using delta-sigma modulation

Analysis of distortion in pulse modulation converters for switching radio frequency power amplifiers

“…The location of the pulse is determined using the quantised phase,θ. The phase modulated signal is then fed to a pulse width modulator where the quantised amplitude,R is converted to duration as in [4]. The equations from [13] are used to decide the amplitude quantisation levels for the polar quantiser.…”

“…Over the years, process technology has improved and it is possible to directly generate the digital drive signals using sigma delta (Σ∆) techniques. Alldigital modulators using bandpass or lowpass Σ∆ modulators have been proposed in [2]- [4]. Fig.…”

“…Two possible techniques that reduce switching activity are the polar Σ∆ [4] and the Cartesian Σ∆ [10]. The polar Σ∆ consists of two lowpass Σ∆s operating on polar representations of the baseband signal, followed by an upconversion block, that performs polar to pulse width modulation (PWM) and pulse position modulation (PPM).…”

“…Often there are no switching pulses, when the input signal is small, thus reducing switching loss which is a principal source of power loss in the amplifier. However, in [4], it was mentioned that a number of spurious tones were observed in the output spectrum. The problem was attributed to non-linearities in the modulation process.…”

Analysis of Non-Uniform Polar Quantisers in a Sigma Delta Transmitter Architecture

“…This paper considers the replacement of the traditional direct up-conversion architecture by a digital architecture. The proposed new architecture (Fig 1(bottom)) eliminates many analog components in the transmitter chain and replaces them with a single predominantly digital sigma delta (Σ∆) up-conversion circuit [4]- [6]. The output of which is a discrete representation (-1,1) or as in this paper (-1,0,1) of the modulated carrier signal.…”