Abstract
In this paper, a calibration approach based on transfer function extraction for the Cartesian vector modulator (VM) is presented. Three kinds of VM models-the ideal VM model, the frequency-dependent VM model and the modified frequency-dependent VM model, are introduced in the proposed calibration approach. The calibration approach starts with an initialization of the transfer function of the modified frequency-dependent VM model. Then, the parameters of the transfer function are modified and extracted from the data of the measured transmission state (transmission amplitude and phase) of the actual VM by iteration, until the transmission state predicted by the extracted transfer function agrees well with the measured transmission state. Subsequently, the extracted transfer function of the modified frequency-dependent VM model is capable of describing the transmission characteristics of the actual VM, and the calibrated baseband control voltages for the desired transmission amplitude and phase of the actual VM are able to be obtained by using the extracted transfer function. An actual VM is used as an example to verify this method. By adopting the proposed method, the maximum amplitude and phase errors at different complex gain setpoints are reduced to 0.05 dB and 0.3° respectively after only two iteration steps. Since the actual VM is able to be accurately calibrated in only a few iteration steps, the results reveal that high accuracy and efficiency can be obtained in this calibration technique, which is well suited for applications involving high-accuracy calibration, real-time calibration and multichannel VM system calibration.
Highlights
The vector modulator (VM) plays an important role in a variety of applications, in which the amplitude and phase control of signals are required, in beamforming and phased array systems [1]–[3], modern communication systems [4]–[6], fifth-generation (5G) mobile technology [7]–[10], and feed-forward linearization techniques [11]–[13].Traditionally, the VM can be divided into four main categories [6], [14], [15]: polar-based [16], phase oversampling [14], constant-Gm [15], and Cartesian-combining types [6]
A calibration method based on transfer function extraction for the Cartesian VM is presented
In this paper, a calibration method based on transfer function extraction for the Cartesian VM is presented
Summary
The vector modulator (VM) plays an important role in a variety of applications, in which the amplitude and phase control of signals are required, in beamforming and phased array systems [1]–[3], modern communication systems [4]–[6], fifth-generation (5G) mobile technology [7]–[10], and feed-forward linearization techniques [11]–[13]. C. Wang et al.: Calibration Method Based on Transfer Function Extraction for Cartesian VM was implemented by sweeping the control voltages of the VM while measuring its corresponding transmission state, and search through the measured transmission states to find which are closest to the desired transmission states. When high-resolution and high-accuracy along with large control range are desired for the transmission states, a small step size and a large sweep area would be required for the I and Q control voltages This would result in a large number of testing points on the control voltage plane, leading to a time-consuming and inefficient measurement. The transfer functions of the modified frequency-dependent VM model are able to be accurately extracted from the measured transmission amplitude and phase of the actual VM.
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