Switched capacitor based harmonic rejection mixer with the clocks having two different duty cycles
A harmonic rejection mixer that uses switched capacitors for amplitude control and uses two different duty cycle local oscillator (LO) signals for phase control for each harmonic. The harmonic rejection mixer uses 2-vector variable duty harmonic rejection. which allows for the harmonic rejection mixer to be less complex. consume less power, and/or use less components/space compared to conventional harmonic rejection mixers.
1. A radio frequency (RF) transmitter comprising:
a harmonic rejection mixer comprising:
a first switch to receive an I-path differential baseband input signal, wherein the first switch is to be controlled by a first I-path differential local oscillator (LO) signal having a 50 percent duty cycle;
a second switch to receive the I-path differential baseband input signal, wherein the second switch is to be controlled by a second I-path differential LO signal having a 25percent duty cycle;
a third switch to receive a Q-path differential baseband input signal, wherein the third switch is to be controlled by a first Q-path differential LO signal having a 25 percent duty cycle;
a fourth switch to receive the Q-path differential baseband input signal, wherein the fourth switch is to be controlled by a second Q-path differential LO signal having a 50 percent duty cycle;
a first output capacitor coupled to the first switch, wherein the first output capacitor has a first capacitance;
a second output capacitor coupled to the second switch and the third switch, wherein the second output capacitor has a second capacitance that is larger than the first capacitance by a multiple of a scaling factor; and
a third output capacitor coupled to the fourth switch, wherein the third output capacitor has the first capacitance.
2. The RF transmitter of claim 1 , wherein the scaling factor is √2 or 1.4.
3. The RF transmitter of claim 1 , wherein the harmonic rejection mixer further includes a gain control capacitor to provide conversion gain control.
4. The RF transmitter of claim 1 , wherein the harmonic rejection mixer is to generate an output voltage according to the following equation:
V
out
=
A
·
(
Rect
50
%
(
t
)
+
S
·
Rect
25
%
(
t
)
)
·
V
ini
+
A
·
(
Rect
50
%
(
t
+
T
0
4
)
+
S
·
Rect
25
%
(
t
+
T
0
4
)
)
·
V
inq
wherein V out is the output voltage, V ini is an I-path input voltage, V inq is a Q-path input voltage, S is the scaling factor, Rect50% (t) is a rectangular waveform with respect to time t having a 50 percent duty cycle, Rect25% (t) is a rectangular waveform with respect to time t having a 25 percent duty cycle, T 0 is a period of the rectangular waveforms having the 50 percent duty cycle and 25 percent duty cycle, and
A
=
C
S
·
C
+
C
+
C
+
C
load
,
wherein C is the first capacitance and C load is a capacitance of a load capacitor.
5. The RF transmitter of claim 1 , wherein one period of the first I-path differential LO signal, the second I-path differential LO signal, the first Q-path differential LO signal, and the second Q-path differential LO signal includes eight phases.
6. The RF transmitter of claim 1 , further comprising:
a LO signal generator to generate the first I-path differential LO signal, the second I-path differential LO signal, the first Q-path differential LO signal, and the second Q-path differential LO signal.
7. The RF transmitter of claim 6 , wherein the LO signal generator comprises:
a frequency divider circuit to generate an 8-phase signal having a 50 percent duty cycle; and
a twenty five and fifty percent (25/50%) generator circuit coupled to the frequency divider circuit to generate a LO signal having 25 percent duty cycle based on the 8-phase signal having 50 percent duty cycle generated by the frequency divider circuit.
8. The RF transmitter of claim 7 , wherein the 25%/50% generator circuit comprises:
a first AND logic circuit to perform a logical AND operation on a 45 degree phase and 315 degree phase of the 8-phase signal having the 50 percent duty cycle;
a second AND logic circuit to perform a logical AND operation on a 135 degree phase and 270 degree phase of the 8-phase signal having the 50 percent duty cycle;
a third AND logic circuit to perform a logical AND operation on a 45 degree phase and 135 degree phase of the 8-phase signal having the 50 percent duty cycle;
a fourth AND logic circuit to perform a logical AND operation on a 225 degree phase and 315 degree phase of the 8-phase signal having the 50 percent duty cycle;
a fifth AND logic circuit to perform a logical AND operation on a 0 degree phase of the 8-phase signal having the 50 percent duty cycle;
a sixth AND logic circuit to perform a logical AND operation on a 90 degree phase of the 8-phase signal having the 50 percent duty cycle;
a seventh AND logic circuit to perform a logical AND operation on a 180 degree phase of the 8-phase signal having the 50 percent duty cycle; and
an eighth AND logic circuit to perform a logical AND operation on a 270 degree phase of the 8-phase signal having the 50 percent duty cycle.
9. The RF transmitter of claim 1 , wherein the harmonic rejection mixer is to use 2-vector modulation, wherein a first vector of the 2-vector modulation represents a waveform having a 25 percent duty cycle multiplied by the scaling factor and a second vector of the 2-vector modulation represents a waveform having a 50 percent duty cycle.
10. The RF transmitter of claim 1 , further comprising: a power amplifier coupled to an output of the harmonic rejection mixer.
11. A harmonic rejection mixer comprising:
a first switch to receive an I-path differential baseband input signal, wherein the first switch is to be controlled by a first I-path differential local oscillator (LO) signal having a 50 percent duty cycle;
a second switch to receive the I-path differential baseband input signal, wherein the second switch is to be controlled by a second I-path differential LO signal having a 25 percent duty cycle;
a third switch to receive a Q-path differential baseband input signal, wherein the third switch is to be controlled by a first Q-path differential LO signal having a 25 percent duty cycle;
a fourth switch to receive the Q-path differential baseband input signal, wherein the fourth switch is to be controlled by a second Q-path differential LO signal having a 50 percent duty cycle;
a first output capacitor coupled to the first switch, wherein the first output capacitor has a first capacitance;
a second output capacitor coupled to the second switch and the third switch, wherein the second output capacitor has a second capacitance that is larger than the first capacitance by a multiple of a scaling factor; and
a third output capacitor coupled to the fourth switch, wherein the third output capacitor has the first capacitance.
12. The harmonic rejection mixer of claim 11 , wherein the scaling factor is √2 or 1.4.
13. The harmonic rejection mixer of claim 11 , further comprising:
a gain control capacitor to provide conversion gain control.
14. The harmonic rejection mixer of claim 11 , wherein an output voltage is to generated according to the following equation:
V
out
=
A
·
(
Rect
50
%
(
t
)
+
S
·
Rect
25
%
(
t
)
)
·
V
ini
+
A
·
(
Rect
50
%
(
t
+
T
0
4
)
+
S
·
Rect
25
%
(
t
+
T
0
4
)
)
·
V
inq
wherein V out is the output voltage, V ini is an I-path input voltage, V inq is a Q-path input voltage, S is the scaling factor, Rect50% (t) is a rectangular waveform with respect to time t having a 50 percent duty cycle, Rect25% (t) is a rectangular waveform with respect to time t having a 25 percent duty cycle, T 0 is a period of the rectangular waveforms having the 50 percent duty cycle and 25 percent duty cycle, and
A
=
C
S
·
C
+
C
+
C
+
C
load
,
wherein C is the first capacitance and C load is a capacitance of a load capacitor.
15. The harmonic rejection mixer of claim 11 , wherein one period of the first I-path path differential LO signal, the second I-path differential LO signal, the first Q-path differential LO signal, and the second Q-path differential LO signal includes eight phases.