RF Transmit Path Calibration via On-Chip Dummy Load

Abstract

Methods and devices are described for calibrating RF transmit paths of an RF front-end stage with minimum transmitted RF power at an output port of the RF front-end stage. Furthermore, an integrated RF switch with a terminating switchable load is presented which can be used to terminate a transmit path at the point of termination for measuring an RF signal at that point.

1 . A radio frequency (RF) circuital arrangement configured to transmit an RF signal at an output RF transmit port via one or more RF transmit paths, wherein a transmit path of the one or more transmit RF paths comprises:
 one or more adjustable RF devices configured during operation to affect one or more characteristics of the RF signal; and   a terminating switch positioned between an adjustable RF device of the one or more adjustable RF devices and the output RF transmit port,   wherein:   during a first mode of operation of the RF transmit path, the terminating switch is configured to couple the RF signal to the output RF transmit port, and   during a second mode of operation of the RF transmit path, the terminating switch is configured to isolate the RF signal from the output RF transmit port and terminate the RF signal into a terminating load connected to a terminating terminal of the terminating switch.   
     
     
         2 . The RF circuital arrangement of  claim 1 , further comprising an output switch, wherein the output switch is configured to couple a selected RF transmit path of the plurality of RF transmit paths to the output RF transmit port and isolate a remaining RF transmit paths of the plurality of RF transmit paths from the output RF transmit port. 
     
     
         3 . The RF circuital arrangement of  claim 1 , wherein an isolation provided by the terminating switch with respect to the output RF transmit port during the second mode of operation is equal to or greater than about 25 dB. 
     
     
         4 . The RF circuital arrangement of  claim 2 , wherein a combined isolation provided by the terminating switch and the output switch during the second mode of operation of the RF transmit path of the plurality of RF transmit paths with respect to the output RF transmit port is equal to or greater than about 57 dB when the output switch isolates the transmit path from the output RF transmit port. 
     
     
         5 . The RF circuital arrangement of  claim 1 , wherein during the first mode of operation of the RF transmit path the terminating switch connects the RF signal at a common terminal of the terminating switch to a switching terminal of the terminating switch such as to provide a low resistance conduction path to the output RF transmit port, and wherein during the second mode of operation of the RF transmit path the terminating switch connects the RF signal at the common terminal of the terminating switch to the terminating terminal. 
     
     
         6 . The RF circuital arrangement of  claim 4 , further comprising an RF coupling device operatively coupled to the transmit path of the plurality of transmit paths at a coupling point between the terminating switch and the adjustable RF device, wherein the RF coupling device is configured to sense an RF signal at the coupling point. 
     
     
         7 . The RF circuital arrangement of  claim 6 , further comprising a controller unit configured to select a mode of operation of the RF transmit path and adjust the one or more adjustable RF devices based on a characteristic of the one or more characteristics of a sensed RF signal during the second mode of operation, wherein the mode of operation comprises the first mode of operation and the second mode of operation. 
     
     
         8 . The RF circuital arrangement of  claim 7 , wherein the controller unit is further configured to control the output switch. 
     
     
         9 . The RF circuital arrangement of  claim 7 , wherein the second mode of operation is a calibration mode used to calibrate the selected transmit path and wherein the sensed RF signal is based on an RF test signal of one or more RF test signals suitable for detecting the characteristic of the one or more characteristics of the sensed RF signal. 
     
     
         10 . The RF circuital arrangement of  claim 9 , wherein the controller unit is further configured to generate the one or more RF test signals, and to select, during the calibration mode, the RF test signal of the one or more RF test signals. 
     
     
         11 . The RF circuital arrangement of  claim 9 , wherein an adjustment of the one or more adjustable RF devices during the calibration mode of the selected transmit path provides a desired operating characteristic of the one or more adjustable RF devices for the first mode of operation, wherein the desired operating characteristic is in correspondence of a desired characteristic of the one or more characteristics of the RF signal during the first mode of operation. 
     
     
         12 . The RF circuital arrangement of  claim 9 , wherein during the second mode of operation the controller unit is further configured to control the output switch to isolate the RF transmit path from the output RF transmit port. 
     
     
         13 . The RF circuital arrangement of  claim 9 , wherein the characteristic of the sensed RF signal comprises one or more of: a) an amplitude, b) a power level, c) a DC content, d) linearity, e) a phase shift, f) a harmonic frequency content, and g) an adjacent channel leakage ratio (ACLR) of the sensed RF signal. 
     
     
         14 . A radio frequency (RF) circuital arrangement configured to transmit an RF signal at an output RF transmit port, the RF circuital arrangement comprising:
 an output switch comprising a plurality of switching terminals and a common terminal, wherein the common terminal is operatively coupled to the output RF transmit port;   a plurality of RF transmit paths comprising one or more adjustable RF devices and configured, during operation, to transmit the RF signal, wherein the plurality of RF transmit paths are coupled to the plurality of switching terminals; and   a terminating switch positioned between an adjustable RF device of the one or more adjustable RF devices and the output RF transmit port,   wherein:   during a first mode of operation of the RF circuital arrangement, the terminating switch is configured to couple the RF signal to the output RF transmit port, and   during a second mode of operation of the RF circuital arrangement, the terminating switch is configured to isolate the RF signal from the output RF transmit port and terminate the RF signal into a terminating load connected to a terminating terminal of the terminating switch.   
     
     
         15 . The RF circuital arrangement of  claim 14 , wherein an isolation provided by the terminating switch during the second mode of operation with respect to the output transmit port is equal to or greater than about 25 dB. 
     
     
         16 . The RF circuital arrangement of  claim 14 , wherein during the first mode of operation the output switch is configured to couple the RF signal to the output RF transmit port, and during the second mode of operation the output switch is configured to isolate the RF signal from the RF transmit port. 
     
     
         17 . The RF circuital arrangement of  claim 16 , wherein a combined isolation provided by the terminating switch and the output switch with respect to the output RF transmit port during the second mode of operation is equal to or greater than about 57 dB. 
     
     
         18 . The RF circuital arrangement of  claim 14 , wherein the terminating switch is positioned between the common terminal of the output switch and the output RF transmit port. 
     
     
         19 . The RF circuital arrangement of  claim 18 , further comprising an RF coupling device operatively coupled to the terminating switch at a coupling point, wherein the RF coupling device is configured to sense an RF signal at the coupling point. 
     
     
         20 . The RF circuital arrangement of  claim 19 , wherein the coupling point is positioned between the terminating terminal of the terminating switch and the terminating load. 
     
     
         21 . The RF circuital arrangement of  claim 19 , wherein the coupling point is positioned between the common terminal of the output switch and the common terminal of the terminating switch. 
     
     
         22 . The RF circuital arrangement of  claim 18 , further comprising an isolation switch positioned between the terminating switch and the output RF transmit port. 
     
     
         23 . The RF circuital arrangement of  claim 22 , wherein the terminating switch and the isolation switch combined provide an isolation with respect to the output RF transmit port equal to or greater than about 57 dB. 
     
     
         24 . A monolithically integrated radio frequency (RF) circuit comprising:
 an RF switch comprising a common terminal and a plurality of switching terminals, wherein during operation the switch is adapted to connect a selected switching terminal of the plurality of switching terminals to the common terminal, and   a resistor connected via a first terminal of the resistor, to a terminating switching terminal of the plurality of switching terminals, wherein the RF switch and the resistor are monolithically integrated on a same integrated circuit.   
     
     
         25 . The monolithically integrated RF circuit of  claim 24 , further comprising one or more RF devices comprising of: a) an RF power amplifier, and b) an RF filter network. 
     
     
         26 . The monolithically integrated RF circuit of  claim 25 , wherein an RF device of the one or more RF devices is adjustable. 
     
     
         27 . An RF circuital arrangement comprising the monolithically integrated RF circuit of  claim 24 . 
     
     
         28 . The RF circuital arrangement of  claim 27 , wherein a second terminal of the resistor is connected to one of: a) ground, and b) a measuring device. 
     
     
         29 . The monolithically integrated RF circuit of  claim 24 , wherein the monolithically integrated RF circuit is fabricated using a technology comprising one of: a) silicon on sapphire, b) silicon on insulator, and c) bulk-silicon. 
     
     
         30 . A method for calibrating a transmit path of a radio frequency (RF) front-end stage, the method comprising:
 providing a switchable load impedance in a transmit path;   during a calibration of the transmit path, terminating the transmit path at the switchable load impedance;   based on the terminating, reducing an output RF signal power at an output antenna of the transmit path;   based on the terminating, measuring an RF signal characteristic at the switchable load impedance;   based on the measuring, adjusting an adjustable RF device of the transmit path, and   based on the adjusting, calibrating the transmit path,   wherein the reducing provides an output RF signal power at the output antenna of the transmit path lower than a desired RF transmission power.   
     
     
         31 . The method of  claim 30 , wherein the desired RF transmission power is a locally regulated unintentional RF transmission power. 
     
     
         32 . The method of  claim 30 , wherein the reducing provides an output RF signal power at the output antenna of at least 57 dB below an output RF signal power at the output antenna when the transmit path is not terminated at the switchable load impedance. 
     
     
         33 . The method of  claim 32 , wherein the terminating further comprises switching an antenna switch such as further reducing the output RF signal power at the output antenna. 
     
     
         34 . A method for calibrating a transmit path of a radio frequency (RF) front-end stage, the method comprising:
 providing an RF front-end stage comprising one or more transmit paths, wherein each transmit path of the one or more transmit paths is adapted to be connected to a transmit port via an output RF switch;   providing one or more RF switches, wherein an RF switch of the one or more RF switches is adapted to provide a series connection between two RF components of a transmit path of the plurality of transmit paths via a common terminal of the RF switch and a first switching terminal of the RF switch;   selecting a transmit path of the plurality of transmit paths for transmission of an RF signal at the transmit port;   configuring the output switch to connect the selected transmit path to the output port;   configuring at least a subset of the one or more RF switches to provide series connections between two RF components of the selected transmit path;   providing the RF signal to the selected transmit path;   transmitting the RF signal based on the providing of the RF signal;   calibrating the selected transmit path by performing the following steps:
 i) configuring an RF switch of the one or more RF switches to disable a series connection between two RF components of the selected transmit path, 
 ii) based on the configuring, terminating the selected transmit path at a resistor load connected to a second switching terminal of the RF switch, 
 iii) sensing an RF signal at the resistor load, 
 iv) based on the sensing, adjusting an adjustable RF component of the selected transmit path, and 
 v) configuring the RF switch of the one or more RF switches to provide series connection between the two RF components of the transmit path; and 
   based on the calibrating, obtaining a desired signal characteristic of the transmitted RF signal.   
     
     
         35 . The method of  claim 34 , further comprising maintaining the desired signal characteristic by repeating the calibrating of the selected transmit path. 
     
     
         36 . The method of  claim 34 , wherein the desired signal characteristic comprises one or more of: a) an amplitude, b) a power level, c) a DC content, d) linearity, e) a phase shift,  0  a harmonic frequency content, and g) an adjacent channel leakage ratio (ACLR) of the transmitted RF signal.