Documentation Center |
Model mixer and local oscillator using Z-parameters
The Z-Parameters Mixer block models the nonlinear mixer described in the block dialog box in terms of its frequency-dependent Z-parameters, the frequencies of the Z-parameters, noise data (including phase noise data), and nonlinearity data.
The Z-parameter values all refer to the mixer input frequency.
The Z-Parameters Mixer block uses the RF Toolbox™ z2s function to convert the Z-parameters to S-parameters and then interpolates the resulting S-parameters to determine their values at the modeling frequencies. See SimRF Equivalent Baseband Algorithms for more details.
SimRF™ Equivalent Baseband software computes the reflected wave at the mixer input ( ) and at the mixer output ( ) from the interpolated S-parameters as
where
and are the mixer input and output frequencies, respectively.
and are the incident waves at the mixer input and output, respectively.
The interpolated S_{21} parameter values describe the conversion gain as a function of frequency, referred to the mixer input frequency.
You can specify active block noise in one of the following ways:
Spot noise data in the Z-Parameters Mixer block dialog box.
Noise figure, noise factor, or noise temperature value in the Z-Parameters Mixer block dialog box.
If you specify block noise as spot noise data, the block uses the data to calculate noise figure. The block first interpolates the noise data for the modeling frequencies, using the specified Interpolation method. It then calculates the noise figure using the resulting values.
The Z-Parameters Mixer block applies phase noise to a complex baseband signal. The block first generates additive white Gaussian noise (AWGN) and filters the noise with a digital FIR filter. It then adds the resulting noise to the angle component of the input signal.
The blockset computes the digital filter by:
Interpolating the specified phase noise level to determine the phase noise values at the modeling frequencies.
Taking the IFFT of the resulting phase noise spectrum to get the coefficients of the FIR filter.
Note: If you specify phase noise as a scalar value, the blockset assumes that the phase noise is the phase noise is constant at all modeling frequencies and does not have a 1/f slope. This assumption differs from that made by the Mathematical Mixer block. |
You can introduce nonlinearities into your model by specifying parameters in the Nonlinearity Data tab of the Z-Parameters Mixer block dialog box. Depending on which of these parameters you specify, the block computes up to four of the coefficients , , , and of the polynomial
that determines the AM/AM conversion for the input signal . The block automatically calculates , the linear gain term. If you do not specify additional nonlinearity data, the block operates as a mixer with a linear gain. If you do, the block calculates one or more of the remaining coefficients as the solution to a system of linear equations, determined by the following method.
The block checks whether you have specified a value other than Inf for:
The third-order intercept point ( or ).
The output power at the 1-dB compression point ( ).
The output power at saturation ( ).
In addition, if you have specified , the block uses the value for the gain compression at saturation ( ). Otherwise, is not used. You define each of these parameters in the block dialog box, on the Nonlinearity Data tab.
The block calculates a corresponding input or output value for the parameters you have specified. In units of dB and dBm,
where is in units of dB.
The block formulates the coefficients , , and , where applicable, as the solutions to a system of one, two, or three linear equations. The number of equations used is equal to the number of parameters you provide. For example, if you specify all three parameters, the block formulates the coefficients according to the following equations:
The first two equations are the evaluation of the polynomial at the points and , expressed in linear units (such as W or mW) and normalized to a 1-Ω impedance. The third equation is the definition of the third-order intercept point.
The calculation omits higher-order terms according to the available degrees of freedom of the system. If you specify only two of the three parameters, the block does not use the equation involving the parameter you did not specify, and eliminates any terms from the remaining equations. Similarly, if you provide only one of the parameters, the block uses only the solution to the equation involving that parameter and omits any or terms.
If you provide vectors of nonlinearity and frequency data, the block calculates the polynomial coefficients using values for the parameters interpolated at the center frequency.
Z-parameters for a nonlinear mixer in a 2-by-2-by-M array. M is the number of Z-parameters.
Frequencies of the Z-parameters as an M-element vector. The order of the frequencies must correspond to the order of the Z-parameters in Z-Parameters. All frequencies must be positive. The following figure shows the correspondence between the Z-parameters array and the vector of frequencies.
The method used to interpolate the network parameters. The following table lists the available methods describes each one.
Method | Description |
---|---|
Linear (default) | Linear interpolation |
Spline | Cubic spline interpolation |
Cubic | Piecewise cubic Hermite interpolation |
Type of mixer. Choices are Downconverter (default) and Upconverter.
Local oscillator frequency. If you choose Downconverter, the blockset computes the mixer output frequency, f_{out}, from the mixer input frequency, f_{in}, and the local oscillator frequency, f_{lo}, as f_{out} = f_{in} – f_{lo}. If you choose Upconverter, f_{out} = f_{in} + f_{lo}.
Note: For a downconverting mixer, the local oscillator frequency must satisfy the condition f_{in} – f_{lo} ≥ 1/(2t_{s}), where t_{s} is the sample time specified in the Input Port block. Otherwise, an error appears. |
Vector specifying the frequency offset.
Vector specifying the phase noise level.
Type of noise data. The value can be Noise figure, Spot noise data, Noise factor, or Noise temperature. This parameter is disabled if the data source contains noise data.
Scalar ratio or vector of ratios, in decibels, of the available signal-to-noise power ratio at the input to the available signal-to-noise power ratio at the output, (S_{i}/N_{i})/(S_{o}/N_{o}). This parameter is enabled if Noise type is set to Noise figure.
Minimum scalar ratio or vector of minimum ratios of the available signal-to-noise power ratio at the input to the available signal-to-noise power ratio at the output, (S_{i}/N_{i})/(S_{o}/N_{o}). This parameter is enabled if Noise type is set to Spot noise data.
Optimal mixer source impedance. This parameter is enabled if Noise type is set to Spot noise data. The value can be a scalar or vector.
Resistance or vector of resistances normalized to the resistance value or values used to take the noise measurement. This parameter is enabled if Noise type is set to Spot noise data.
Scalar ratio or vector of ratios of the available signal-to-noise power ratio at the input to the available signal-to-noise power ratio at the output, (S_{i}/N_{i})/(S_{o}/N_{o}). This parameter is enabled if Noise type is set to Noise factor.
Equivalent temperature or vector of temperatures that produce the same amount of noise power as the mixer. This parameter is enabled if Noise type is set to Noise temperature.
Scalar value or vector corresponding to the domain of frequencies over which you are specifying the noise data. If you provide a scalar value for your noise data, the block ignores the Frequency (Hz) parameter and uses the noise data for all frequencies. If you provide a vector of values for your noise data, it must be the same size as the vector of frequencies. The block uses the Interpolation method specified in the Main tab to interpolate noise data.
Type of third-order intercept point. The value can be IIP3 (input intercept point) or OIP3 (output intercept point). This parameter is disabled if the data source contains power data or IP3 data.
Value of third-order intercept point. This parameter is disabled if the data source contains power data or IP3 data. Use the default value, Inf, if you do not know the IP3 value. This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).
Output power value ( ) at which gain has decreased by 1 dB. This parameter is disabled if the data source contains power data or 1-dB compression point data. Use the default value, Inf, if you do not know the 1-dB compression point. This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).
Output power value ( ) that the mixer produces when fully saturated. This parameter is disabled if the data source contains output saturation power data. Use the default value, Inf, if you do not know the saturation power. If you specify this parameter, you must also specify the Gain compression at saturation (dB). This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).
Decrease in gain ( ) when the power is fully saturated. The block ignores this parameter if you do not specify the Output saturation power (dBm). This parameter can be a scalar (to specify frequency-independent nonlinearity data) or a vector (to specify frequency-dependent nonlinearity data).
Scalar or vector value of frequency points corresponding to the third-order intercept and power data. This parameter is disabled if the data source contains power data or IP3 data. If you use a scalar value, the IP3 (dBm), 1 dB gain compression power (dBm), and Output saturation power (dBm) parameters must all be scalars. If you use a vector value, one or more of the IP3 (dBm), 1 dB gain compression power (dBm), and Output saturation power (dBm) parameters must also be a vector.
For information about plotting, see Create Plots.