RF detector with crest factor measurement
An RF detector configured to provide two outputs, one being a function of the true RMS power level of an RF input signal, and the other being a function of the instantaneous/peak power of the RF input signal, normalized to the average power level. The RF detector includes a variable gain detection subsystem including a single detector or detector array that provides a representation of the power level of the RF input signal. The detector or detector array is common to both the RMS power detection channel and the instantaneous/peak power detection channel of the RF detector. A method of RF detection includes providing representations of the RF input signal at different gain levels, selecting one or more of the representations, and averaging the selected signals. The gain levels of the selected representations is adjusted to provide information about the average power level of the RF input signal.
1. A power detector comprising:
an input configured to receive an input signal;
one squaring detector coupled to the input and configured to detect the input signal and to provide a detector output signal;
an averaging circuit coupled to the squaring detector and configured to receive the detector output signal and to provide a first signal which is representative of an average power level of the input signal;
an instantaneous power processing device coupled to the squaring detector and configured to receive the detector output signal and to provide at an output of the power detector an instantaneous power output signal which is representative of the instantaneous power level of the input signal normalized to a representation of the average power level of the input signal.
2. The power detector of claim 1 , wherein the averaging circuit is further configured to receive a reference signal and to adjust a scaling factor of the squaring detector based on an average difference between the detector output signal and the reference signal to adjust an average of the detector output signal to a level approximately that of the reference signal.
3. The power detector of claim 1 , further comprising a bias control circuit coupled between the averaging circuit and the squaring detector, the bias control circuit being configured to receive the first signal and to provide a detector gain control signal to the squaring detector, the detector gain control signal controlling scaling of the squaring detector based on the first signal.
4. The power detector of claim 1 , further comprising a variable gain amplifier coupled between the input and the squaring detector, the variable gain amplifier being configured to receive the first signal and to provide an amplified output signal;
wherein a gain of the variable gain amplifier is controlled by the first signal; and
wherein the squaring detector is configured to receive the amplified output signal.
5. The power detector of claim 1 , wherein the instantaneous power processing device comprises:
a transistor follower configured to receive the detector output signal and to provide the instantaneous power output signal; and
a network coupled to the transistor follower and configured to compensate for temperature variation of the base-emitter voltage of the transistor follower to provide a substantially temperature stable instantaneous power output signal.
6. The power detector of claim 5 , wherein the network comprises a plurality of transistors and at least two resistors including a first resistor and a second resistor;
wherein a base of the transistor follower is coupled to a node between the first resistor and the second resistor.
7. The power detector of claim 6 , wherein the transistors are bipolar transistors.
8. The power detector of claim 6 , wherein the transistors are field effect transistors.
9. The power detector of claim 5 , wherein the instantaneous power processing device further comprises a capacitor coupled to the transistor follower, the capacitor configured to store a voltage representative of a peak signal level at an output of the transistor follower.
10. A method of power detection comprising:
receiving an input signal at an input of a detector;
detecting with the detector a power level of the input signal to provide a detected signal;
subtracting from the detected signal a signal not related to the input signal to reduce effects of temperature and fabrication process variations at an output of the detector and to provide an output signal;
averaging the output signal and providing an error signal representative of an average power level of the input signal; and
providing an instantaneous power output signal responsive to the output signal, the instantaneous power output signal being representative of the instantaneous power level of the input signal normalized to a representation of the average power level of the input signal.
11. The method of claim 10 , further comprising adjusting a scaling factor of the detector based on the error signal.
12. The method of claim 10 , wherein providing the instantaneous power output signal includes buffering the output signal using a transistor follower to provide the instantaneous power output signal.
13. The method of claim 12 , further comprising compensating for temperature variation of a base-emitter voltage of the transistor follower to provide a substantially temperature stable instantaneous power output signal.
14. The method of claim 10 , wherein subtracting from the detected signal the signal not related to the input signal includes subtracting from the detected signal a signal generated by a reference detector which does not receive the input signal.