Digital aided clipping methods and devices for digital power amplifier
Methods and wireless communication devices for adaptive clipping input of a Digital Power Amplifier (DPA). The wireless communication device receives a baseband sample with In-phase (I) and Quadrature-phase (Q) components and clips the baseband sample upon determining that the baseband sample satisfies a clipping condition. The clipping condition is satisfied when a sum of absolute values of the I and Q components is greater than a predefined threshold value, and after clipping, a sum of absolute values of the I and Q components becomes less than or equal to the predefined threshold value. The methods and wireless communication devices drive the DPA to generate a Radio Frequency (RF) output for wireless transmission according to the clipped baseband sample to prevent mirror image distortion.
1 . A digital clipping method for adaptive clipping input of a Digital Power Amplifier (DPA) in a wireless communication device, the method comprising:
receiving an In-phase (I) component and a Quadrature-phase (Q) component of a baseband sample, wherein the I and Q components are represented by digital codes;
determining whether the baseband sample satisfies a clipping condition, wherein the clipping condition is satisfied when a sum of absolute values of the I and Q components is greater than a predefined threshold value, and wherein the predefined threshold value is determined depending on a number of bits of the digital code for representing the I or Q component of the baseband sample;
upon the baseband sample satisfies the clipping condition, clipping the baseband sample and thereby a sum of absolute values of the I and Q components of the clipped baseband sample is less than or equal to the predefined threshold value; and
driving the DPA according to the baseband sample to generate a Radio Frequency (RF) output for wireless transmission.
2 . The digital clipping method of claim 1 , wherein N bits are used to represent an amplitude of the digital code for the I or Q component, and the predefined threshold value is 2 to the power of N.
3 . The digital clipping method of claim 2 , wherein 15 bits are used to represent the amplitude of the digital code for the I or Q component, and the predefined threshold value is 32768.
4 . The digital clipping method of claim 3 , wherein the clipping condition is satisfied when |I|+|Q|>32768.
5 . The digital clipping method of claim 1 , wherein clipping the baseband sample further comprises deriving an orthogonal projection of the baseband sample to a clipping rhombus, wherein a sum of absolute values of I and Q components of each value on the clipping rhombus is equal to the predefined threshold value.
6 . The digital clipping method of claim 5 , wherein clipping the baseband sample further comprises:
determining a quadrant the baseband sample belongs to;
determining a slope and an intercept corresponding to the quadrant; and
deriving a clipped sample on the clipping rhombus based on the determined slope and intercept.
7 . The digital clipping method of claim 6 , wherein the clipped baseband sample (X P , Y P ) is derived from the baseband sample (X, Y) that satisfy the clipping condition, the slope (m), and the intercept (c) by:
X
p
=
X
+
m
Y
-
m
c
1
+
m
2
and
Y
p
=
m
X
+
m
2
Y
+
c
1
+
m
2
.
8 . The digital clipping method of claim 7 , wherein the division operation for deriving the clipped baseband sample is implemented by a shift operation.
9 . The digital clipping method of claim 1 , wherein clipping the baseband sample further comprises mapping the baseband sample to a clipped sample according to a mapping table, wherein a sum of absolute values of I and Q components of the clipped sample is equal to or less than the predefined threshold value.
10 . The digital clipping method of claim 1 , wherein clipping the baseband sample further comprises deriving an orthogonal projection on the baseband sample within a clipping rhombus, wherein a sum of absolute values of I and Q components of each value within the clipping rhombus is less than the predefined threshold value.
11 . A wireless communication device transmitting Radio Frequency (RF) signal on a wireless medium, comprising:
a processor;
one or more memory banks, communicatively coupled to the processor and storing processor readable codes that, when executed by the processor, is configured to perform digital clipping; and
a transmitter, comprising:
a digital clipping module, receiving a baseband sample with an In-phase (I) component and a Quadrature-phase (Q) component, determining whether the baseband sample satisfies a clipping condition, and clipping the baseband sample that satisfies the clipping condition, wherein the clipping condition is satisfied when a sum of absolute values of the I and Q components is greater than a predefined threshold value wherein the predefined threshold value is determined depending on a number of bits of respective digital code for representing the I or Q components of the baseband sample, and a sum of absolute values of the I and Q components of the clipped baseband sample is less than or equal to the predefined threshold value; and
a Digital Power Amplifier (DPA) coupled to the digital clipping module,
generating an RF output for wireless transmission according to the baseband sample.
12 . The wireless communication device of claim 11 , wherein the DPA comprises a Switched capacitor Power Amplifier (ScPa).
13 . The wireless communication device of claim 11 , further comprised of a transmit upsampling module for interpolating the baseband sample, resampling to a sub-multiple of RF, and outputting the baseband sample to the digital clipping module.
14 . The wireless communication device of claim 13 , wherein the transmit upsampling module further comprises a mixer for translating a signal around DC to a sub-band offset, and a compensator for compensating transmit IQ imbalance and Local Oscillator (LO) leakage before resampling.