Adaptive CMOS predistortion linearizer for fiber-optic links

Abstract

Nonlinearity in the electrical-to-optical conversion limits the dynamic range for transmitting analog and multilevel signals over fiber-optic channels. We describe a complementary metal-oxide-semiconductor (CMOS) predistortion linearizer that extends the dynamic range of both direct and externally modulated links. The linearizer achieves 13-24-dB suppression for both second-and third-order distortions.

Analysis of Internally Bandlimited Multistage Cubic-Term Generators for RF Receivers

“…Such architectures were not considered for the project in [9] as they are not easily implemented in CMOS processes. CMOS cubic-term generators that utilize the third-order Taylor series coefficients of the MOSFET have also been presented [14]- [16]. However, as the MOSFET is a square-law device, the third-order Taylor series coefficient is relatively weak.…”

“…Memory effects in the predistorted PA system, including nonconstant frequency response over the signal bands of interest, can result in asymmetric upper and lower IM3 sidebands, limiting the achievable error cancellation [14], [18], as shown in Fig. 4.…”

“…For the UMTS FDD specification [22], the required double-sided signal bandwidth to be retained is 3.84 MHz. It can be safely assumed that, based on the achieved linearization bandwidth results of [10], [11], [13], [14], and [16]- [18], maintaining a relatively constant frequency response around this frequency range is, in general, not difficult and that only the minimal frequency response correction is required of the adaptive equalizer.…”

“…Here, the UMTS TX leakage is modeled as sinusoidal blocker #2 (11) (12) The value of can be found via the Taylor series expansion of the MOS short-channel current (13) [23]. To simplify the notation, the equalities in (14) have been substituted (13) (14) Taking the repeated derivatives of (13) yields the following: The power spectral density (PSD) of the thermal noise of the input devices is evaluated using the MOS long-channel noise model. This was done as the simulation models available for this work permitted a more realistic and constant value of the noise parameter over than did the short-channel noise model.…”

Digitally Enhanced Alternate Path Linearization of RF Receivers

“…Ideally, the IM3 products in the alternate path would be produced by the same mechanism as they are in the main path: namely, by the third-order nonlinearity of the MOSFET device. Recently, CMOS cubic predistortion circuits using this design approach have been presented as well [32,33]. Another class of circuits associated with this application is known collectively as polynomial predistorters.…”