A Line Coding for Digital RF Transmitter Using a 1-bit Band-Pass Delta-Sigma Modulator

Abstract

The 1-bit digital radio frequency (DRF) transmitter using a band-pass delta-sigma modulator (BP-DSM) can output a radio frequency (RF) signal carrying a binary data stream with a constant data rate regardless of the carrier frequency, which makes it possible to transmit RF signals over digital optical links with a constant bit rate. However, the optical link requires a line coding, such as 8B10B or 64B66B, to constrain runlength and disparity, and the line coding corrupts the DRF power spectrum owing to additional or encoded data. This paper proposes a new line coding for BP-DSM, which is able to control the runlength and the disparity of the 1-bit data stream by adding a notch filter to the BP-DSM that suppresses the low frequency components. The notch filter stimulates the data change and balances the direct current (DC) components. It is demonstrated that the proposed line coding shortens the runlength from 50 bits to less than 8 bits and reduces the disparity from several thousand bits to 5 bits when the 1-bit DRF transmitter outputs an LTE signal with 5 MHz bandwidth, when using carrier frequencies from 0.5 GHz to 2 GHz and an output power variation of 60 dB.