Method of Correction of the Non-Linear Distortions Entered by an Analog Key in Probing Signals
Keywords:
Method of Digital Correction, Digital Frequency Synthesizer, Analog KeyAbstract
Purpose: Implementation of potential characteristics of any RLS depends on stability of parameters of heterodyne signals and
methods of their formation. Digital synthesizers of frequencies of probing signals are widely applied to form probing signals with
in-out parameters. However in case of digital formation of signals there are non-linear distortions caused by operations of digital-toanalog
conversion and conversion in an analog key which lead to formation of parasitic copies of an oblate signal during coordinated
processing of probing signals in a receiver that, eventually, restricts application of digital synthesizers of frequencies of probing signals
in specialized and multifunctional RLS. One of the effective solutions of this problem is development of a method of correction of nonlinear
distortions entered by an analog key in probing signals. Results: Researches have shown that in a time domain dynamic errors
of conversion are linked to the moments of switching discharges of a control signal by a digital-to-analog converter accordingly and by
the moments of switching levels of quantization of an output signal. This characteristic feature of dynamic errors allows carrying out
a correction of non-linear distortions by means of time gating. The feature is that at the moments of switching levels of quantization
for a time period equal to duration of transient phenomena a digital-to-analog converter is switched off by means of an analog key.
Therefore, dynamic errors of digital-to-analog conversion "enter" from a probing signal. A control signal of an analog key has a time
delay of a relatively clock signal equal to duration of transient phenomena in a digital-to-analog converter and duration of a gating
impulse which does not exceed differences of half a period of a clock signal and a doubled value of duration of transient phenomena.
In its turn, correction of non-linear distortions of a probing signal contributed by an analog key is carried out due to introduction of
pre-distortions into a created signal by means of a digital corrector which transfer function is an inverse transfer function of an analog
key. A generalized transfer function of sequentially connected corrector and analog key is represented a power series with new resultant
coefficients. Retaining a finite number of row members and considering equality to unit of a resultant coefficient at linear row members
and to zero in case of row members with higher degrees is a condition of correction, the obtained recurrence relation for determination
of corrector coefficients is received. Therefore, the proposed method of digital correction of non-linear distortions contributed to a
probing signal by an analog key allows to increase real dynamic range of a digital synthesizer of frequencies of probing signals and to
enhance quality of synthesizable signals. Practical relevance: The method can be used for correction of nonlinear distortions in digital
frequency synthesizers applied in radar-location, communication systems and high-precision measuring equipment.