HB XF Analysis (hbxf)
Description
A conventional transfer function analysis computes the transfer function from every source in the circuit to a single output. Unlike a conventional AC analysis that computes the response from a single stimulus to every node in the circuit, the Harmonic Balance Transfer Function or HBXF analysis computes the transfer functions from any source at any frequency to a single output at a single frequency. Thus, like HBAC analysis, HBXF analysis includes frequency conversion effects.
The HBXF analysis directly computes such useful quantities as conversion efficiency (transfer function from input to output at required frequency), image and sideband rejection (input to output at undesired frequency), and LO feed-through and power supply rejection (undesired input to output at all frequencies).
As with a HBAC, HBSP, and HBNoise analyses, a HBXF analysis must follow a HB analysis.
Syntax
Name [p] [n] ... hbxf parameter=value ...
The optional terminals (p and n) specify the output of the circuit. If you do not specify the terminals, you must specify the output with a probe component.
Parameters
|
Degree of annotation. Possible values are no, title, sweep, status, steps and detailed_hb. |
||
The variable of interest at the output can be voltage or current, and its frequency is not constrained by the period of the large periodic solution. While sweeping the selected output frequency, you can select the periodic small-signal input frequencies of interest by setting either the maxsideband or the sidevec parameter. For a given set of n integer numbers representing the sidebands K1, K2, ... Kn, the input signal frequency at each sideband is computed as f(in)= f(out) + Ki * fund(pss), where, f(out) represents the (possibly swept) output signal frequency and funds(HB) represents the fundamental frequencies used in the corresponding HB analysis. Thus, when analyzing a down-converting mixer and sweeping the IF output frequency, Ki= +1 for the RF input represents the first upper-sideband, while Ki= -1 for the RF input represents the first lower-sideband. By setting the maxsideband value to Kmax, all 2 * Kmax + 1 sidebands from -Kmax to +Kmax are selected.
The number of requested sidebands does not change substantially the simulation time. However, the maxacfreq of the corresponding HB analysis should be set to guarantee that | max{f(in)} | is less than maxacfreq; otherwise, the computed solution might be contaminated by aliasing effects. The HBXF simulation is not executed for | f(out) | greater than maxacfreq. Diagnostic messages are printed for those extreme cases, indicating how maxacfreq should be set in the HB analysis. In majority of simulations, however, this is not an issue, because maxacfreq is never allowed to be smaller than 40x the HB fundamental.
With HBXF, the frequency of the stimulus and of the response are usually different (this is an important area in which HBXF differs from XF). The freqaxis parameter is used to specify whether the results should be output versus the input frequency (in), the output frequency (out), or the absolute value of the input frequency (absin).
You can specify the output with a pair of nodes or a probe component. Any component with two or more terminals can be a voltage probe. When there are more than two terminals, they are grouped in pairs, and you use the portv parameter to select the appropriate pair of terminals. Alternatively, you can simply specify a voltage to be the output by giving a pair of nodes on the HBXF analysis statement.
Any component that naturally computes current as an internal variable can be a current probe. If the probe component computes more than one current, you use the porti parameter to select the appropriate current. It is an error to specify both portv and porti. If neither is specified, the probe component provides a reasonable default.
The stimuli parameter specifies the inputs for the transfer functions. There are two choices. stimuli=sources indicates that the sources present in the circuit should be used. The xfmag parameters provided by the sources may be used to adjust the computed gain to compensate for gains or losses in a test fixture. One can limit the number of sources in hierarchical netlists by using the save and nestlvl parameters. stimuli=nodes_and_terminals indicates that all possible transfer functions should be computed.
This is useful when it is not known in advance which transfer functions are interesting. Transfer functions for nodes are computed assuming that a unit magnitude flow (current) source is connected from the node to ground. Transfer functions for terminals are computed assuming that a unit magnitude value (voltage) source is connected in series with the terminal. By default, the transfer functions from a small set of terminals are computed. If transfer functions from specific terminals are required, specify the terminals in the save statement. You must use the :probe modifier (for example, Rout:1:probe) or specify useprobes=yes on the options statement. If transfer functions from all terminals are required, specify currents=all and useprobes=yes on the options statement.
You can specify sweep limits by specifying the end points, or the center value and span of the sweep. Steps can be linear or logarithmic, and you can specify the number of steps or the size of each step. You can specify a step size parameter (step, lin, log, or dec) to determine whether the sweep is linear or logarithmic. If you do not specify a step size parameter, the sweep is linear when the ratio of stop to start values is less than 10 and logarithmic when this ratio is 10 or greater. Alternatively, you can use the values parameter to specify the values that the sweep parameter should take. If you provide both a specific set of values and a set specified using a sweep range, the two sets are merged and collated before being used. All frequencies are in Hertz.
Return to top