XDB allows you to set up a schematic for measuring, or making other measurements at an X dB compression point, where X is user-specified. This element only functions with the APLAC Harmonic Balance simulator.
|IN||ID of the source port||PORT_P1|
|OUT||ID of the power measurement element||PORT_P2|
|XDB||Amount of dB into compression||dB||1|
|GAIN_TYPE||Method used to compute gain||Linear|
|FUNC_IN||Source input power function, e.g. P("f1")+P("f2")||P("f1")|
|FUNC_OUT||Target output power function, e.g. P("f1")+P("f2")||P("f1")|
|ERR||Maximum allowed error in output power||0.01|
|*MAX_ITER||Maximum number of iterations||100|
|*MIN||Lower limit for the source value (relative to the normal value)||0|
|*MAX||Upper limit for the source value (relative to the normal value)||10000|
|RESET||Reset source nominal value at each sweep point||No|
|GAIN_BACKOFF||Gain backoff (in dB) for small signal gain calculation||dB||-60|
* indicates a secondary parameter
IN: Specifies the ID of the input (source) port, the amplitude of which is modified.
OUT: Specifies the ID of the output measurement element. The output measurement element can be a Port or P_METER3 element.
XDB: Specifies the amount of dB into compression. For instance, if you set it to 3, it sets up the schematic for measuring a 3 dB compression point.
GAIN_TYPE: Specifies the type of gain.
Linear: Computes the compression point from the linear gain.
MaxGain: Computes the compression point from the maximum (for example, the gain expansion region).
FUNC_IN/FUNC_OUT: The frequency to be fetched in symbolic form denoted as a string. For example ("2f1 + 3f2") would indicated the mixing product of 2*f1+3*f2 where f1 and f2 are independent excitation frequencies. Also if should be noted that the syntax (P("f1")+P("f2"))/2 will give the average power of a two tone simulation and P("f1")+P("f2”) will provide the sum of the two fundementals.
MIN: Specifies the minimum scale factor applied to the source. The default value is 0; the same as -800 dBm or 0 W.
MAX: Specifies the maximum scale factor applied to the source. The default value is 10000 which is 10000x the nominal voltage or 10000x the nominal power based on the source.
OPT_METHOD: Sets up the optimization method for APLAC to find the compression point. This setting is unrelated to the optimization methods discussed in “Optimization Methods”.
GAIN_BACKOFF: Sets the power level of the source relative to the nominal value for computing the linear gain of the circuit.
The following figure demonstrates how the XDB element functions. The nominal gain is the gain at the input power level specified on the schematic and should be below the knee of the gain expansion region as shown in the following figure.
The XDB element finds the linear region by reducing the nominal input power by 60 dB, then it finds the maximum gain by raising the input power from the nominal input power. If there is no gain expansion, the nominal gain is used for the maximum gain. The desired compression point is the point X dB below the linear gain if "Linear" is the GAIN_TYPE, and X dB below the maximum gain if "MaxGain" is the GAIN_TYPE. The XDB element always finds the compression point in the compression area (it only looks at input power levels above the input power that produces maximum gain.)
For example, if the nominal gain is 20.2 dB, linear gain is 20 dB, and maximum gain is 22 dB, the 1 dB compression point can have two different answers depending on what you specify. If you select "Linear", the 1 dB compression point is at 20 - 1 = 19 dB, but if you select "MaxGain", the 1 dB compression point is at 22 - 1 = 21 dB. All of these points are shown in the following figure.
This element does not have an assigned layout cell. You can assign artwork cells to any element. See “Assigning Artwork Cells to Layout of Schematic Elements” for details.
The following figure shows an example of how to use the XDB element in a schematic. In this example, the XDB element is set up for 1 dB compression from the linear gain. The PWRSMP element is connected in the schematic to measure the incident input power.
The following figure shows the power and efficiency for the previous schematic. Because the XDB element is present in the schematic, the power added efficiency, input power, and output power are all calculated at the 1 dB gain compression point. This is why the input power changes vs. frequency.
If the same schematic is simulated without the XDB element, it results in the following figure. In this case, the input power is constant, similarly, the output power and PAE are computed at the user-specified input power.