Voltage Mapping in Envelope Tracking Measurement

Voltage Mapping is an important concept and digital process in envelope tracking measurement, involving parameters in several blocks. This section illustrates the detailed relationships in the related parameters. Most of the envelope tracking algorithm and terminology used in this section is compliant to MIPI eTrak spec.

Voltage mapping involves three blocks:

• Envelope Tracking block

  In this block, shaping table is specified. Shaping table defines the relationship between input column (RF Voltage) and the supply voltage of the PA (V_cc). The input column can be Normalized I/Q Amplitude, Absolute RF Output Voltage of the input signal or Override Absolute RF.

• Envelope Signal Generator block

  In this block, Voltage is calculated through voltage mapping process and Voltage Offset is also set in the process.

  If the Envelope Signal Generator in use is N5172B EXG or N5172B MXG, another setting Peak Voltage will be calculated instead of Voltage.

• ETPS

  In this block, two parameters for the PA are set: ETPS Gain and V_cc Offset and one parameter defined in MIPI eTrak spec is set: V_CM.

To introduce voltage mapping, two sections are included:

Voltage Mapping Concepts

Voltage Mapping Procedure in N7614B

Voltage Mapping Concepts

Equation 1 shows the relationships of the related parameters, which is from eTrak spec.

where,

V_cc is the supply voltage of the PA, which is also called V_{ETPS_OUT} in eTrak spec.

V_{cc_offset} is the Vcc Offset parameter in ETPS block. This parameter can be measured at the ETPS output by setting V_REF to 0.

ETPS_GAIN is the amplification of the differential supply voltage, which corresponds to ETPS Gain setting in ETPS block.

V_ETP is the positive signal output of the Envelope Signal Generator.

V_ETN is the negative signal output of the Envelope Signal Generator.

V_REF is used as the reference for ETPS.

V_CM is the common mode voltage as defined in MIPI eTrak spec.

The following figure illustrates the relationship between V_ETP, V_ETN, V_REF, and V_CM clearly.

Voltage Mapping Procedure in N7614B

In N7614B Signal Studio for Power Amplifier Test, voltage mapping works as follows:

1. Use the shaping table defined in Envelope Tracking block to calculate the supply voltage of PA (V_cc) from the RF voltage of the signal.

   

2. Calculate V_REF using a transformation of equation 1 as shown in equation 2. Note that V_{CC_offset} and ETPS_GAIN values are set in ETPS block.

   

3. Calculate the single port Voltage value for Envelope Signal Generator block using equation 3.

   

   in which V_{REF_MAX} is the maximum value of V_REF, V_{REF_MIN} is the minimum value of V_REF.

   The Voltage Offset value in Envelope Signal Generator block is equal to the V_CM value in ETPS block. V_CM parameter is independent from the parameters discussed above and can be set by the user as required.
   If the Envelope Signal Generator in use is N5172B EXG or N5172B MXG, another setting Peak Voltage will be used instead of Voltage.