Wideband receiver robust to radio frequency harmonics
View Patent ↗A radio frequency (RF) noise-cancelling receiver includes first transconductance cells configured to produce respective weighted current signals proportional to an input voltage signal. The RF receiver includes frequency conversion cells coupled to the first transconductance cells and configured to mix the weighted current signals with a plurality of non-overlapping local oscillator (LO) signals to produce downconverted current signals. The RF receiver includes transimpedance amplifiers coupled to the frequency conversion cells and configured to produce output voltage signals proportional to the downconverted current signals. The transimpedance amplifiers include second transconductance cells. Each of the first and second transconductance cells has an effective transconductance of a first magnitude for frequency components of the input voltage signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the input voltage signal arising from harmonics at integer multiples of the first harmonic.
1. A radio frequency (RF) receiver comprising:
a first set of transconductance cells configured to produce respective weighted current signals proportional to an input voltage signal;
a plurality of frequency conversion cells coupled to the first set of transconductance cells and configured to mix the weighted current signals with a plurality of non-overlapping local oscillator (LO) signals to produce downconverted current signals; and
a plurality of transimpedance amplifiers coupled to the plurality of frequency conversion cells and configured to produce output voltage signals proportional to the downconverted current signals, wherein the plurality of transimpedance amplifiers comprise a second set of transconductance cells, each input to the plurality of transimpedance amplifiers being coupled to each output of the plurality of frequency conversion cells,
wherein each of the first set and second set of transconductance cells has an effective transconductance of a first magnitude for frequency components of the input voltage signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the input voltage signal arising from harmonics at integer multiples of the first harmonic.
2. The RF receiver of claim 1 , wherein each of the first and second sets of transconductance cells is configured with a transconductance weighting that causes the effective transconductance of the transconductance cell to be non-zero when excited by received signals arising from a harmonic within a frequency band of interest and zero for received signals arising from harmonics outside the frequency band of interest.
3. The RF receiver of claim 2 , wherein the transconductance weighting provides that wanted harmonics cause a current change through the transconductance cell.
4. The RF receiver of claim 1 , wherein the first and second sets of transconductance cells are configured to amplify a received signal from any harmonic of a fundamental frequency.
5. The RF receiver of claim 4 , wherein the first and second sets of transconductance cells are further configured to amplify a received signal from more than one harmonic multiple of the fundamental frequency.
6. The RF receiver of claim 1 , wherein the plurality of frequency conversion cells and the first set of transconductance cells employ single-ended inputs.
7. The RF receiver of claim 6 , wherein each of the first and second sets of transconductance cells comprises a set of transconductance weighting equal to
gmx
=
k
[
1
+
cos
(
2
π
X
M
)
]
,
where X is an integer that represents each of the transconductance cells, M is a number of LO phases employed, and k is an arbitrary constant that determines the effective transconductance of the transconductance cell.
8. The RF receiver of claim 1 , wherein the plurality of frequency conversion cells and the first set of transconductance cells employ differential inputs.
9. The RF receiver of claim 8 , wherein each of the first and second sets of transconductance cells comprises a set of transconductance weighting equal to
gmx
=
k
[
cos
(
2
π
X
M
)
]
,
where X is an integer that represents each of the transconductance cells, M is a number of LO phases employed, and k is an arbitrary constant that determines the effective transconductance of the transconductance cell.
10. The RF receiver of claim 1 , wherein the plurality of non-overlapping LO signals have successive phase shifts substantially equal to 360/M degrees, where M is a number of LO phases employed.
11. The RF receiver of claim 10 , wherein the plurality of non-overlapping LO signals each have a fundamental frequency.
12. The RF receiver of claim 11 , wherein the number of LO phases corresponds to a number of harmonics relative to the fundamental frequency.
13. The RF receiver of claim 12 , wherein each of the second set of transconductance cells receives M downconversion signals including an input coupled to ground, where M is the number of LO phases employed based on the number of harmonics corresponding to the fundamental frequency with a magnitude greater than a threshold magnitude.
14. The RF receiver of claim 1 , wherein each of the second set of transconductance cells receives a voltage input equivalent to
V
IN
∠
m
*
(
M
-
1
)
M
,
where m is a LO harmonic from around which the input voltage signal originated, and M represents a number of LO phases employed.
15. A receiver for wideband applications, comprising:
an integrated circuit pin configured to couple a radio frequency (RF) signal to a first signal path and a second signal path;
a plurality of transconductance cells configured to produce weighted current signals proportional to the RF signal along the first signal path and the second signal path, wherein each of the plurality of transconductance cells has an effective transconductance of a first magnitude for frequency components of the RF signal arising from a first harmonic and an effective transconductance of a second magnitude less than the first magnitude for frequency components of the RF signal arising from harmonics at integer multiples of the first harmonic;
a plurality of mixers configured to mix the weighted current signals with local oscillator (LO) signals of successive phase shifts to generate mixer signals; and
a feedback impedance coupled to at least a portion of the plurality of transconductance cells along the first signal path to convert the mixer signals into corresponding voltage signals, each input to the at least a portion of the plurality of transconductance cells being coupled to each output of the plurality of mixers.
16. The receiver of claim 15 , wherein each of the plurality of transconductance cells is further configured with a transconductance gain that shifts the weighted current signal with a defined phase such that a constructive sum of the weighted current signals provides a resulting current signal of a selected phase.
17. The receiver of claim 16 , wherein the plurality of mixers and the plurality of transconductance cells employ single-ended inputs, and wherein the transconductance gain is shifted to reject any integer multiple of a wanted signal corresponding to the first harmonic.
18. The receiver of claim 16 , wherein the plurality of mixers and the plurality of transconductance cells employ differential inputs, and wherein the transconductance gain is shifted to reject odd integer multiples of a wanted signal corresponding to the first harmonic.
19. The receiver of claim 15 , wherein each of the plurality of transconductance cells alone the second signal path receives an input voltage signal equivalent to
V
IN
∠
m
*
(
M
-
1
)
M
,
where m is a LO harmonic from around which the input voltage signal originated, and M represents a number of LO phases employed.
20. The receiver of claim 15 , further comprising a plurality of transimpedance amplifiers along the second signal path, wherein each of the plurality of transimpedance amplifiers comprises at least a portion of the plurality of transconductance cells.