Digital detector utilizable in providing closed-loop gain control in a transmitter
A digital detector processes at least one received digital signal to generate a squared signal, encodes the squared signal, applies first and second portions of the encoded signal to a multiplier and a look-up element, respectively, and processes outputs of the multiplier and look-up element to generate a detector output signal representative of a power level of the received digital signal. In an illustrative embodiment, the digital detector is configured so as to exhibit a waveform dependence substantially the same as that of an analog logarithmic amplifier detector. The digital detector and analog logarithmic amplifier detector are utilizable in a closed-loop gain control arrangement for providing a desired gain for a signal path of a base station transmitter in a wireless communication system.
1. A digital detector comprising:
a first signal processing element configured to receive at least one digital signal and to generate a squared signal therefrom;
an encoder having an input coupled to an output of the first signal processing element, and operative to generate an encoded signal from the squared signal;
a multiplier and a look-up element, the multiplier and the look-up element receiving respective first and second portions of the encoded signal; and
a second signal processing element configured to process outputs of the multiplier and the look-up element to generate a detector output signal representative of a power level of the at least one digital signal.
2. The digital detector of claim 1 wherein the first signal processing element comprises at least one squaring element.
3. The digital detector of claim 2 wherein the first signal processing element comprises a first squaring element for squaring a first digital signal, a second squaring element for squaring a second digital signal, and a summing element for summing the squares of the first and second digital signals.
4. The digital detector of claim 3 wherein the first and second digital signals comprise one or more samples of baseband in-phase (I) and quadrature (Q) digital signals, respectively.
5. The digital detector of claim 1 wherein the encoder comprises a floating-point encoder, the first and second portions of the encoded signal corresponding to respective first and second portions of a floating-point number.
6. The digital detector of claim 5 wherein the encoder generates an N-bit floating-point number, a first output of the encoder corresponding to the first portion of the floating-point number and coupled to an input of the multiplier is representative of an exponent of the floating-point number, and a second output of the encoder corresponding to the second portion of the floating-point number and coupled to an input of the look-up element is representative of a mantissa of the floating-point number.
7. The digital detector of claim 5 wherein the floating-point number comprises a number of the form Y=I 2 +Q 2 , where I and Q denote respective baseband in-phase and quadrature digital signals received by the first signal processing element.
8. The digital detector of claim 1 wherein the multiplier is operative to generate a product of a scale factor and the first portion of the encoded signal in order to determine a logarithm of the first portion of the encoded signal.
9. The digital detector of claim 1 wherein the look-up element comprises a look-up table utilizable to determine a logarithm of the second portion of the encoded signal.
10. The digital detector of claim 1 wherein the second signal processing element comprises:
a summing element having first and second inputs coupled to respective outputs of the multiplier and the look-up element; and
an accumulator having an input coupled to an output of the summing element, the accumulator being operative to accumulate output signal values generated by the summing element over multiple samples of the at least one digital signal.
11. The digital detector of claim 1 wherein the detector output signal representative of a power level of the at least one digital signal is of the form:
C
·
log
(
Y
)
=
C
·
log
(
2
k
·
(
1
+
Y
0
/
2
p
)
)
=
C
·
log
(
2
)
·
k
+
C
·
log
(
1
+
Y
0
/
2
p
)
where Y is an N-bit floating-point number corresponding to the encoded signal generated by the encoder, k is a most significant non-zero bit of Y and represents an exponent of the floating-point number, p denotes a number of bits in a mantissa Y 0 of the floating-point number, and C is a constant specifying a slope of the digital detector.
12. The digital detector of claim 1 wherein the digital detector is configured to generate an output signal representative of a root-mean-squared (RMS) power level of the at least one digital signal.
13. The digital detector of claim 1 wherein the digital detector is configured so as to exhibit a waveform dependence substantially the same as that of an analog logarithmic amplifier detector.
14. The digital detector of claim 1 wherein one or more of the first and second signal processing elements, the encoder, the multiplier and the look-up element are implemented at least in part in software running on a processor.
15. The digital detector of claim 14 wherein the processor comprises a baseband processor of a base station transmitter in a wireless communication system.
16. A transmitter comprising a gain control feedback loop incorporating the digital detector of claim 1 .
17. The transmitter of claim 16 wherein the transmitter comprises a base station transmitter in a wireless communication system.
18. The transmitter of claim 16 wherein the transmitter comprises:
baseband circuitry operative to generate the at least one digital signal;
radio frequency circuitry having an input coupled to an output of the baseband circuitry;
a power amplifier having an input coupled to an output of the radio frequency circuitry;
an analog detector;
a coupler configured to couple a portion of an amplified signal from an output of the power amplifier to an input of the analog detector; and
a gain control circuit;
the output signal of the digital detector being supplied as a first input to the gain control circuit, the analog detector generating an output signal that is supplied as a second input to the gain control circuit, the gain control circuit generating a gain control output utilized to control at least one gain control element of a radio frequency path comprising the radio frequency circuitry and the power amplifier.
19. A method for use in a digital detector, the method comprising the steps of:
generating a squared signal from at least one received digital signal;
encoding the squared signal;
applying first and second portions of the encoded signal to a multiplier and a look-up element, respectively; and
generating a detector output signal representative of a power level of the received digital signal, utilizing outputs of the multiplier and look-up element.
20. An article of manufacture comprising a machine-readable storage medium for storing one or more programs for use in implementing at least a portion of a digital detector, wherein the one or more programs when executed perform the steps of:
generating a squared signal from at least one received digital signal;
encoding the squared signal;
applying first and second portions of the encoded signal to a multiplier and a look-up element, respectively; and
generating a detector output signal representative of a power level of the received digital signal, utilizing outputs of the multiplier and look-up element.