U.S. patent application number 16/135965 was filed with the patent office on 2020-03-19 for compact architecture for multipath low noise amplifier.
The applicant listed for this patent is pSemi Corporation. Invention is credited to Jonathan James Klaren.
Application Number | 20200091876 16/135965 |
Document ID | / |
Family ID | 68069922 |
Filed Date | 2020-03-19 |
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United States Patent
Application |
20200091876 |
Kind Code |
A1 |
Klaren; Jonathan James |
March 19, 2020 |
Compact Architecture for Multipath Low Noise Amplifier
Abstract
Methods and devices used in mobile receiver front end to support
multiple paths and multiple frequency bands are described. The
presented devices and methods provide benefits of scalability,
frequency band agility, as well as size reduction by using one low
noise amplifier per simultaneous outputs. Based on the disclosed
teachings, variable gain amplification of multiband signals is also
presented.
Inventors: |
Klaren; Jonathan James; (San
Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
pSemi Corporation |
San Diego |
CA |
US |
|
|
Family ID: |
68069922 |
Appl. No.: |
16/135965 |
Filed: |
September 19, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H03F 2200/489 20130101;
H03F 2200/225 20130101; H03F 2200/135 20130101; H03F 2200/294
20130101; H03G 1/0088 20130101; H03F 2200/243 20130101; H03F
2200/222 20130101; H03G 5/165 20130101; H03F 2200/297 20130101;
H03F 2200/48 20130101; H03F 2200/387 20130101; H03F 2200/391
20130101; H03F 2200/301 20130101; H03F 2200/451 20130101; H03F
2200/546 20130101; H04B 1/16 20130101; H03F 2200/111 20130101; H03F
2200/156 20130101; H03F 2200/42 20130101; H03F 2200/75 20130101;
H03F 2200/216 20130101; H03F 3/195 20130101; H03F 2200/378
20130101; H03F 3/193 20130101; H03F 2200/61 20130101; H03F 3/68
20130101; H03F 2200/213 20130101; H03F 2200/492 20130101; H03G
3/001 20130101; H03F 2200/429 20130101; H03F 2200/72 20130101; H03G
5/28 20130101 |
International
Class: |
H03F 3/195 20060101
H03F003/195; H03F 3/68 20060101 H03F003/68; H04B 1/16 20060101
H04B001/16 |
Claims
1. A radio frequency (RF) receiver comprising: a plurality of
current gain blocks; and a plurality of output loads; wherein: (i)
each current gain block is selectively connected to one or more
output loads of the plurality of the output loads; (ii) a current
gain block of the plurality of current gain blocks is configured
to: receive an input signal; generate one or more amplified signals
corresponding to the input signal, and (iii) an output load of the
plurality of output loads is configured to receive corresponding
one or more amplified signals and to generate corresponding one or
more output signals.
2. The RF receiver of claim 1, wherein the plurality of current
gain blocks and the plurality of output loads are implemented on a
same chip or die.
3. The receiver of claim 1, wherein: the plurality of current gain
blocks are tunable; the input signal corresponds to one or more
frequency bands; and the current gain block of the plurality of
current gain blocks is further configured to tune into the one or
more frequency bands.
4. The RF receiver of claim 3, wherein the output loads are tunable
supporting a second frequency band including a combination of the
one or more first frequency bands supported by corresponding
current gain blocks.
5. The RF receiver of claim 1, wherein each current gain block of
the plurality of current gain blocks comprises: one or more gain
transistors; a first variable capacitor coupled across gate and
source of a gain transistor of the one or more gain transistors;
one or more cascode transistors coupling the one or more gain
transistors to corresponding one or more output loads of the
plurality of output loads; and drains of the one or more cascode
transistors are connectable to a power supply via an RF choke.
6. The RF receiver of claim 1, wherein each current gain block of
the plurality of current gain blocks comprises: one or more gain
transistors; a first variable inductor coupling sources of the one
or more gain transistors to a first reference voltage or ground;
one or more cascode transistors coupling the one or more gain
transistors to corresponding one or more output loads of the
plurality of output loads; and drains of the one or more cascode
transistors are connectable to a power supply via an RF choke.
7. The RF receiver of claim 5, wherein each current gain block of
plurality of current gain blocks further comprises a first variable
inductor coupling sources of the one or more gain transistors to a
first reference voltage or ground.
8. The RF receiver of claim 7, wherein a combination of the
variable capacitor and the variable inductor is used to tune a
corresponding current gain block to a corresponding one or more
frequency bands.
9. The RF receiver of claim 8, wherein a combination of the
variable capacitor and the variable inductor is used to set a
desired gain and impedance adapted to the corresponding one or more
frequency bands.
10. The RF receiver of claim 7, wherein the output loads comprise:
an RF choke; and a transistor stack coupling the cascode
transistors to a second variable inductor coupled to a second
reference voltage or ground;.
11. The RF receiver of claim 7, wherein the output loads comprise
an RF choke; and a transistor stack and a second variable
capacitor; wherein the second variable capacitor couples the
transistor stack to output terminals of the output load;
12. The RF receiver of claim 11, wherein: the transistor stack
couples the cascode transistors to a second variable inductor
coupled to a second reference voltage or ground; and a combination
of the second variable conductor and the second variable capacitor
is used for tuning purposes.
13. The RF receiver of claim 12, wherein the transistor stack
comprises PMOS transistors.
14. The RF receiver of claim 13, configured to receive bias
voltages via gates of the cascode transistors.
15. The RF receiver of claim 14, wherein the cascode transistors
are configured to be in ON or OFF states in correspondence with
applied bias voltages.
16. The RF receiver of claim 15, wherein each output load is
configured to receive an amplified signal from only one of
corresponding current gain blocks of the plurality of current gain
blocks.
17. The RF receiver of claim 1, wherein at least one current gain
block of the plurality of current gain blocks is different from all
other current gain blocks of the plurality of gain blocks.
18. The RF receiver of claim 1, wherein all current gain blocks of
the plurality of current gain blocks are the same.
19. The RF receiver of claim 1, wherein each current gain block of
the plurality of current gain blocks is different from any other
gain block of the plurality of current gain blocks.
20. The RF receiver of claim 7, wherein at least one of the current
gain blocks of the plurality of current gain blocks has a variable
gain.
21. The receiver of claim 12, further comprising a first switch and
a second switch configured to control a signal through the current
gain block wherein: the first switch is coupled across a
combination of the gain transistors and the cascode transistors;
the second switch couples an input terminal to an output terminal;
in a first gain state, the first switch is closed and the second
switch is open, thereby bypassing the one or more gain transistors,
and creating a first signal path from the input terminal to the
output terminal through the transistor stack; in a second gain
state, the first switch is open and the second switch is open,
thereby bypassing the stacked transistors and creating a second
signal path from the input terminal to the output terminal via a
combination of the one or more gain transistors and the one or more
cascode transistors; and in a third state, the first switch is open
and the second switch is closed, thereby creating a third path
directly from the input terminal to the output terminal without
amplification.
22. The receiver of claim 12, further comprising a first switch and
a second switch configured to control a gain of the current gain
block wherein: the first switch is coupled across a combination of
the gain transistors and the cascode transistors, the second switch
is coupled across the stacked transistors; in a first state, the
first switch is closed, and the second switch is open, thereby
creating a first signal path from the input terminal to the output
terminal through the stacked transistors; in a second state, the
first switch is open and the second switch is closed, thereby
bypassing the stacked transistors and creating a second signal path
from the input terminal to the output terminal via a combination of
the one or more gain transistors and the one or more cascode
transistors; and in a third state, the first switch and the second
switch are closed, thereby bypassing the stacked transistors and
the gain transistors and creating a third signal path from the
input terminal to the output terminal.
23. A method of amplifying a signal with a spectrum comprising
multiple frequency bands: providing one or more current gain
blocks; providing one or more output loads; connecting each gain
block of the one or more current gain blocks to one or more output
loads; amplifying at least one signal corresponding to one or more
frequency bands of the multiple frequency bands to generate one or
more amplified signals, and driving at least one output loads of
the one or more output loads using the one or more amplified
signals to generate at least one or more amplified output
signals.
24. The method of claim 23, wherein the one or more amplified
output signals comprises two or more amplified output signals.
25. A radio frequency (RF) receiver front end comprising: a
plurality of band filters corresponding to one or more frequency
bands representing an input signal; one or more band switches; one
or more current gain blocks connecting each a corresponding band
switch of the one or more band switches to one or more output
loads; wherein: each band switch is configured to select at least
one frequency band filter of the plurality of band filters; a
current gain block corresponding to the band switch is configured
to selectively tune into the at least one frequency band of the one
or more frequency bands; the at least one frequency band filter of
the one or more frequency band filters receives the input signal to
generate a filtered signal; the current gain block is configured to
receive the filtered signal to generate one or more amplified
signals; and the one or more output loads are configured to receive
the one or more amplified signals and to generate corresponding one
or more output signals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is related to U.S. Pat. No.
9,941,849 issued Apr. 10, 2018, entitled "Programmable Optimized
Band switching LNA for Operation in Multiple Narrow-Band Frequency
Ranges", application Ser. No. 15/616,824 filed Jun. 7, 2017,
entitled "LNA with Variable Gain and Switched Degeneration
Inductor", U.S. Pat. No. 9,973,149 issued May 15, 2018, entitled
"Source Switched Split LNA", and application Ser. No. 15/846,055
filed Dec. 18, 2017, entitled "Switchless Multi Input Stacked
Transistor Amplifier Tree Structure", all incorporated herein by
reference in their entirety.
BACKGROUND
Technical Field
[0002] The present disclosure is related to low noise amplifiers
(LNA), and more particularly to methods and apparatus used in
mobile receiver front end to support multiple paths and multiple
frequency bands.
Background
[0003] Low noise amplifier (LNA) front end circuits for mobile
communication continue to increase in complexity requiring support
for multiple frequency bands and for multiple amplifier paths
active at the same time (carrier aggregation and/or dual
connectivity). As an example, in the Long Term Evolution (LTE)
standard, carrier aggregation is used to increase the bandwidth.
Such carrier aggregation may comprise various operation modes such
as intra-band continuous/non-continuous carrier aggregation and
inter-band carrier aggregation. As a result, receivers supporting
these various modes are needed. At the same time, RF front end
suppliers are pushed to make design changes rapidly while reducing
device size and cost. In other words, demand for reducing the size
and manufacturing costs of mobile communication equipment is ever
increasing while miniaturization of such equipment has become an
essential design requirement.
SUMMARY
[0004] Methods and devices taught in the present disclosure address
the challenging and conflicting design requirements described in
the previous section. The described methods and devices provide LNA
designs allowing for easier modifications of the band inputs and
the number of supported outputs. Such methods and devices aim to
reduce the device size by essentially using one LNA per
simultaneous outputs.
[0005] According to a first aspect of the present disclosure, a
radio frequency (RF) receiver is provided comprising: a plurality
of current gain blocks; and a plurality of output loads; wherein:
(i) each current gain block is selectively connected to one or more
output loads of the plurality of the output loads; (ii) a current
gain block of the plurality of current gain blocks is configured
to: receive an input signal; generate one or more amplified signals
corresponding to the input signal, and (iii) an output load of the
plurality of output loads is configured to receive corresponding
one or more amplified signals and to generate corresponding one or
more output signals.
[0006] According to a second aspect of the present disclosure, a
method of amplifying a signal with a spectrum comprising multiple
frequency bands is provided comprising: providing one or more
current gain blocks; providing one or more output loads; connecting
each gain block of the one or more current gain blocks to one or
more output loads; amplifying at least one signal corresponding to
one or more frequency bands of the multiple frequency bands to
generate one or more amplified signals, and driving at least one
output loads of the one or more output loads using the one or more
amplified signals to generate at least one or more amplified output
signals.
[0007] According to a third aspect of the present disclosure, a
radio frequency (RF) receiver front end is provided comprising: a
plurality of band filters corresponding to one or more frequency
bands representing an input signal; one or more band switches; one
or more current gain blocks connecting each a corresponding band
switch of the one or more band switches to one or more output
loads; wherein: each band switch is configured to select at least
one frequency band filter of the plurality of band filters; a
current gain block corresponding to the band switch is configured
to selectively tune into the at least one frequency band of the one
or more frequency bands; the at least one frequency band filter of
the one or more frequency band filters receives the input signal to
generate a filtered signal; the current gain block is configured to
receive the filtered signal to generate one or more amplified
signals; and the one or more output loads are configured to receive
the one or more amplified signals and to generate corresponding one
or more output signals.
DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 shows a receiver front end according to an embodiment
of the present disclosure.
[0009] FIG. 2 shows how different elements of a receiver front end
may be laid out on a same chip or die in accordance with the
present disclosure.
[0010] FIG. 3 shows correspondence of frequencies and output load
supported by various current gain blocks of a receiver front
end.
[0011] FIG. 4 shows some exemplary frequency bands.
[0012] FIGS. 5A-5B show a receiver input stage.
[0013] FIG. 5C shows an exemplary current gain block using stacked
transistors.
[0014] FIG. 5D shows an exemplary receiver front end according to
embodiments of the present disclosure.
[0015] FIG. 6A shows an exemplary LNA architecture according to
embodiments of the present disclosure.
[0016] FIG. 6B shows an exemplary LNA architecture according to
further embodiments of the present disclosure.
[0017] FIG. 7 shows an exemplary LNA architecture with three
different gain states.
[0018] FIG. 8 shows an exemplary LNA architecture with three
different gain states.
DETAILED DESCRIPTION
Definitions
[0019] The term "current gain block" is referred herewith to an
electronic circuit that amplifies an input signal thereby
generating current to drive an output load.
[0020] The term "folded architecture" is referred herewith to an
LNA architecture using a combination of negative metal oxide (NMOS)
and positive metal oxide (PMOS) transistors in current gain and
load stages to provide support for smaller available power supply
voltage headroom imposed by design requirements.
Description
[0021] Methods and devices in accordance with the present
disclosure are presented, providing LNA designs allowing for easier
modifications of the band inputs and the number of supported
outputs. Such methods and devices: [0022] offer band agility,
covering as many bands as possible with one LNA [0023] aim toward
size reduction by using one LNA per simultaneous outputs [0024]
support step-variable gain for low Noise Figure (NF) in high gain
states and high linearity in low gain states.
[0025] FIG. 1 shows a receiver front end (100) according to an
embodiment of the present disclosure. The receiver front end (100)
comprises an antenna (110) connected to a plurality of band filters
(112) through antenna switch (111). The plurality of band filters
(112) correspond to bands (for example, f1, . . . , f4). The
receiver front end (100) further comprises two band switches (113,
114) connected to their corresponding current gain blocks (117,
118) via coupling inductors (115, 116) respectively. According to
an embodiment of the present disclosure, current gain blocks (117,
118) may each be configured to drive two loads (119, 120)
simultaneously and therefore generate output signals at outputs
(out1, out2). Current gain block (117) may be configured to support
either of frequency bands (f1, f2) and similarly, current gain
block (118) may be configured to support either of frequency bands
(B3, B4). Therefore, receiver front end (100) may support four
input bands and two output loads. By way of example, and depending
on design requirements, current blocks (117, 118) may be tuned to
support frequency bands (f1, f3) respectively. In the same
embodiment, band switches (113, 114) may be configured to select
frequency bands (f1, f3) respectively. The person skilled in the
art will appreciate that, depending on design requirements, no
major change in the design of the current gain blocks will be
required except for shifting to the desired frequency band and this
will allow accommodating various design requirements without going
through long design cycles. With further reference to FIG. 1, the
person skilled in the art will also understand that a combination
of, for example, current gain block (117) with each of the loads
(119, 120) may be seen as separate LNA's. By virtue of separating
the current gain block and the loads, a reuse of the same current
gain block simultaneously with multiple output loads has been made
possible, resulting in a reduced foot print to address stringent
size reduction requirements as described previously. With further
reference to FIG. 1, the person skilled in the art will understand
that, without departing from the scope and the spirit of the
invention, embodiments may be made supporting an arbitrary number
of frequency bands, and using arbitrary numbers of current gain
blocks and output loads.
[0026] FIG. 2 shows a diagram (200) of an RF receiver front end
(210) showing how the current gain blocks and output loads may be
laid out on a same chip or die in accordance with an embodiment of
the disclosure. This is a simplified diagram wherein details of how
various elements are interconnected are not shown to avoid
overwhelming the diagram with interconnection details. As shown in
FIG. 2, the RF receiver front end (210) comprises a plurality of
current gain blocks (gm1, . . . , gm6) and output loads (LD1, . . .
, LD4). In other words, the embodiment shown in FIG. 2, supports 6
LNA inputs (each LNA input can support multiple sub-band inputs,
defined by corresponding filters, where the multiple sub-band
inputs can be combined together by a switch or other method) and 4
outputs. Similarly to what was described with regards to receiver
front end (100) of FIG. 1, current gain stages (gm1, . . . , gm6)
may be configurable to tune to various frequency bands. Moreover,
in accordance with further embodiments of the present disclosure,
and depending on the application requirements, each of current gain
blocks (gm1, . . . , gm6) may be connected to one or more of output
loads (LD1, . . . , LD4). This provides benefits of flexibility,
scalability and reusability of the receiver front end (210) for
different applications imposing distinctive requirements. In other
words, a generic floor plan is provided wherein by implementing
minor changes and/or customization to one or more current gain
stages and related interconnections to the loads, the frond end
receiver (210) may be adapted to new applications/requirements
without having to go through a new full design cycle of such a
receiver front end. To further clarify this point, reference is
made to table (300) of FIG. 3 showing frequency coverage of current
gain blocks (gm1, . . . , gm6) of FIG. 2. Table (300) also shows
which output load, each of the current gain blocks (gm1, . . . ,
gm6) are connected to. For example, current gain block (gm5) is
configured to support a frequency band including 2.5 GHz and to
connect to output loads (LD1, . . . , LD4). Continuing with the
same example, the person skilled in the art will appreciate that
current gain block (gm2) may be designed to be reconfigurable
(programmed on the fly) to support multiple frequency bands.
Additionally, designs having distinct gm blocks per band may also
be envisaged in accordance with embodiments of the present
disclosure. For this example, and based on the application
requirement, current gain block (gm5) is tuned to a frequency band
including the center frequency of 2.5 GHz. As another example,
current gain block (gm1) may be configured to support a frequency
band including the center frequency of 1.5 GHz and to connect to
output loads (LD1, LD2, LD3) simultaneously. In view of the above,
embodiments may be envisaged in accordance with the present
disclosure, wherein a plurality of input frequency bands are
supported, and each current gain block may drive one or more output
loads simultaneously. In other words, by virtue of the current gain
blocks and output loads being separate and independent, scalable
designs with the capability of supporting various frequency bands
is made possible by the teachings of the present disclosure.
[0027] With further reference to FIGS. 2-3, the person skilled in
the art will appreciate that, after performing some
adjustments/customization, the receiver front end (200), after
being laid out as shown in FIG. 2, may be reused for different
applications that have similar form factor requirements. By way of
example, and with reference to table (300) of FIG. 3, if a new
application does not require a connection of current gain (gm3) to
output load (1oad2), a customization, including disconnection of
related metals and tying them off to ground, can be implemented to
erase such connection and therefore to adapt the receiver front end
(200) of FIG. 2 to the new application. The person skilled in the
art will understand that such customization is easier and more
straightforward to implement compared to a full redesign of the
whole receiver front end. Moreover, the layout may be designed such
that base layers are configured to support a range of match
component sizes and to support various frequency bands. In view of
this, the teachings of the present disclosure provide design
flexibility, by decreasing time and effort to add/remove band
inputs and simultaneous outputs.
[0028] With further reference to FIG. 3, and according to some
embodiments of the present disclosure, output loads (LD1, . . . ,
LD4) are tunable to support a frequency band including a
combination of frequency bands supported by corresponding current
gain blocks. According to further embodiments of the present
disclosure, one or more of the current gain blocks connected with a
particular output load may be inactive while the other current gain
blocks connected with the particular output load are active. More
in particular, and according to other embodiments of the present
disclosure, the current gain blocks connected to a particular load
are only active one at a time. As an example, and referring to FIG.
3, current gain blocks (gm1, . . . , gm5) are connected to load
LD2. In operative conditions, current gain block (gm1) drives load
(LD1), while other current gain blocks (gm2, . . . , gm5) may be
inactive/OFF, meaning no current is driven to load (LD1) by current
gain blocks (gm2, . . . , gm5). According to further embodiments of
the present disclosure, multiple loads may be active at a time,
each with one active and operating gain block.
[0029] FIG. 4 shows an example of frequency bands that may be
supported by a receiver front end in accordance with embodiments of
the present disclosure. As shown in FIG. 4, current gain blocks
(gm1, . . . , gm5) may be tuned respectively to 1.2 GHz, 1.8 to 1.9
GHz, 2.2 to 2.3 GHz, 2.5.about.2.6 GHz and 3.5.about.3.8 GHz.
According to further embodiments of the disclosure, any output load
connected with current gain blocks (gm1, . . . , gm5) may be
designed to support broader frequency bands compared with of
current gain block. As an example, and with further reference to
FIG. 4, an output load may be designed to support the range 1.2
GHz.about.3.8 GHz.
[0030] A combination of FIGS. 5A-5B shows a receiver input stage
(500AB) comprising current gain blocks (gm1, . . . , gm6) (FIG. 5A)
and output loads (LD1, . . . , LD4) (FIG. 5B). Current gain blocks
(gm1, . . . , gm6) receives input signals from their corresponding
input terminals (in1, . . . , in6). As shown in FIG. 5A, each of
current gain blocks (gm1, . . . , gm6) may be connected to any of
output loads (LD1, . . . , LD4) through connection points (load1, .
. . , load4). As an example, the connection point load1 (of FIG.
5A) of the current gain block gm2 is connected to the connection
point load1 (of FIG. 5B) of the output load LD1. In other words,
the receiver input stage (500A) may receive six different inputs
from terminals (in1, . . . , in6) and each of current gain blocks
(gm1, . . . , gm6) may drive one or more of output loads (LD1, . .
. , LD4) (FIG. 5B 500B) simultaneously, to provide output signals
at output terminals (out1, . . . , out4). Reference is made to FIG.
2 of application Ser. No. 15/846,055 filed Dec. 18, 2017, entitled
"Switchless Multi Input Stacked Transistor Amplifier Tree
Structure", incorporated herein by reference in its entirety,
showing a split LNA, wherein the cascosde split may be applied to
each of current gain blocks (gm1, . . . , gm6) of FIG. 5A, thereby
letting the output connect to one of output loads (LD1, . . . ,
LD4) or two of such output loads if the current gain blocks are
connected using the switch (235) of FIG. 2 of the
above-incorporated reference.
[0031] With reference to FIG. 5A, current gain blocks (gm1, . . . ,
gm6) have similar functionalities and operate based on a similar
concept, although corresponding constituents of each current gain
block may be different from a size and/or performance parameters
stand point. For the sake of clarity and in order to avoid
overwhelming the diagrams, numerals corresponding to constituent
elements of only one of the current gain blocks (e.g. gm1) are
shown in FIG. 5A. Similarly, and making reference to FIG. 5B,
output loads (LD1, . . . , LD4) operate based on the same concept
and have similar functionalities. Therefore, numerals corresponding
to constituent elements of output load (LD1) only is shown in FIG.
5B for the sake of clarity and ease of read. According to
embodiments of the present disclosure, and similarly to what
described with regards to current gain blocks (gm1, . . . , gm6) of
FIG. 5A, corresponding constituent elements of each of output loads
(LD1, . . . , LD4) may be different from one another, with
reference, for example to size, performance parameters, type (for
example inductance vs. capacitance), or whether or not they are
present. Moreover, an embodiment may also be designed wherein
constituents of each of the output loads may comprise one or more
inductances or capacitances or a combination thereof.
[0032] With reference to current gain block (gm1) of FIG. 5A, an
input signal is coupled to gain transistors (T1, T2) through
coupling capacitance C1 and coupling inductance L1. Current gain
block (gm1) comprises two pairs of cascode transistors (T3, T4) and
(T5, T6) with respect to the gain transistors (T1,T2). Cascode
transistors (T3, T4) have their sources coupled with a drain of
corresponding gain transistor T1 and their drains to corresponding
output loads (LD1, LD2) of FIG. 5B at connection points (load1,
load2). Similarly, sources of cascode pair (T5, T6) are connected
to a drain of corresponding gain transistor (T2) and drains of the
cascode pair (T5, T6) are connected to output loads (LD3, LD4) of
FIG. 5B at the connection points (load3, load4). Current gain block
(gm1) further comprises a variable capacitor (Cgs) and a variable
inductor (Ls), a combination of which is used for tuning purposes
to optimize RF performance. According to embodiments of the present
disclosure, current gain stages (gm1, . . . , gm6) may be built
using the same or different constituents. By way of example,
corresponding transistors from one current gain block to another,
may have same or different sizes. In accordance with further
embodiments of the present disclosure, a bias voltage (not shown in
FIG. 5A) is provided to gates of each of the cascode transistors
(T3, T4) and (T5, T6). The bias voltage values applied to the gates
of the cascode transistors (T3, . . . , T6) may all be the same or
different from one another depending on the requirements. During
operative conditions and depending on the bias voltage values one
or more of cascode transistors (T3, . . . , T6) may be inactive/OFF
thus not driving any current to corresponding output loads. More in
particular, when a current gain block is connected to a particular
load through one of the cascode transistors, the bias voltages of
other cascode transistors are such that no other input is going to
that particular load. To further clarify this point, and with
reference to FIG. 5A, when current gain block (gm1) is active and
providing current to output load1 (LD1), no other input is provided
through current gain blocks (gm2, . . . , gm6) to output load1
(LD1). This is implemented by adjusting bias voltage values of
gates of cascode transistors (T3) of current gain blocks (gm2, . .
. , gm6). In other words, only one of the current gain blocks is
connected to a selected output load through a corresponding cascode
transistor.
[0033] With continued reference to FIG. 5A, and similarly to what
is described with regards to embodiments of FIGS. 1-2, current gain
blocks (gm1, . . . , gm6) may be designed to be tunable to one or
more frequency bands. Depending on a specific application
requirement, each current gain block (gm1, . . . , gm6) may be
selected to be to tuned to a specific frequency band and tuned away
from one of the multiple frequency bands each block can be tuned
to. An input impedance (Zin) of current gain block (gm1) of FIG. 5A
may be calculated according to:
Re ( Z in ) = .omega. L s C gs ##EQU00001##
where the term "Re" represents the real part and .omega. is an
angular frequency. The above-mentioned formula may be used to set a
desired gain and impedance adapted for a given frequency band. As
mentioned previously, each current gain block (gm1, . . . , gm6)
may be designed to have various states corresponding to various
frequency bands. Depending on the receiver requirement, one of such
frequency bands may be chosen to be tuned into. For a different
application, different parameter values may be used to support a
potentially new and different frequency band.
[0034] Referring to FIG. 5B, output load (LD1) comprises two
stacked transistors (T7, T8), an RF choke (L3) connecting a supply
voltage (Vdd) to a source of the transistor (T7), and a variable
inductor (L4) and a variable capacitor (C2), a combination of which
is used to tune the output load (LD1) to desired frequency bands. A
first end of the variable inductor (L4) is connected to the
variable capacitor (C2) and to a drain of the transistor (T8),
while a second end of the variable inductor (L4) may be connected
to a reference voltage or ground. In accordance with an embodiment
of the present disclosure, transistors (T1, . . . , T6) of FIG. 5A
are NMOS transistors and transistors (T7, T8) are PMOS transistors.
According to an embodiment of the present disclosure, RF choke (L3)
is used to drive current and has negligible impact on the design
for desired frequency bands. As such, RF choke (L3) may be made
sufficiently large with metallization so that its shunt impedance
does not affect the load impedance. Moreover, according to
embodiments of the present disclosure the RF choke (L3) may be a
current source or an element exhibiting high impedance at the RF
frequency. With further reference to FIG. 5A, and without departing
from the spirit and scope of the invention, embodiments in
accordance with the present disclosure may be envisaged wherein
each of transistors (T1, . . . , T6) comprises a plurality of
stacked transistors. FIG. 5C shows a current gain block (500C) to
illustrate such embodiments. In other words, each pair of
transistor pairs (T1, T1'), . . . , (T6, T6') represents stacked
transistors.
[0035] Referring back to FIG. 5A, the person skilled in the art
will appreciate that further embodiment in accordance with the
present disclosure with one or more inputs, one or more outputs and
supporting one or more frequency bands may be designed. To further
illustrate this, FIG. 5D shows an exemplary receiver front end
(500D) with two inputs (in1, in2) and two outputs (out1, out2). The
receiver front end (500D) further comprises current gain stages
(gm1, gm2) connected to output loads (LD1, LD2) via connections
points (load1, 1oad2). As shown in FIG. 5D, current gain stage
(gm1) may be used to drive one load (e.g. LD1) while current gain
stage (gm2) may be used to drive two loads (LD1, LD2),
simultaneously or only one. According to an embodiment of the
present disclosure, current gain stages (gm1, gm2) may each be
designed to be tunable to one or more arbitrary frequency bands.
Continuing with the same example, portions of the schematic
representing current gain stages (gm1, gm2) of FIG. 5D are shown in
dotted lines. This is to compare the current gains (gm1, gm2) of
FIG. 5D with their counterparts in FIG. 5A and to show the portions
of the current gains of FIG. 5A that have been removed to design
current gains (gm1, gm2) of FIG. 5D.
[0036] FIG. 6A shows an LNA (650) comprising a current gain block
(610) and an output load (611) in accordance with an embodiment of
the present disclosure. Making further reference to FIGS. 5A-5B,
and in view of what described with regards to receiver input stage
(500A & 500B), the LNA (650) represents essentially a
combination of any of current gain blocks (gm1, . . . , gm6) of
receiver input stage (500A) with any of output loads (LD1, . . . ,
LD4) of the receiver input stage (500B). According to an embodiment
of the present disclosure, transistor (T61, T62) are NMOS
transistors and transistors (T64, T63) are PMOS transistors. The
person skilled in art will appreciate that LNA (650) has a folded
architecture allowing to accommodate possible stringent voltage
headroom requirements. By virtue of using different transistor
types for transistor pairs (T61, T62) and (T63, T64), design
requirements imposing smaller available voltage headroom may be
supported. According to embodiments of the present disclosure, the
output load (611) may comprises one or more cascode
transistors.
[0037] FIG. 6B shows an LNA (651) in accordance with a further
embodiment of the present disclosure. Similar to the LNA (650) of
FIG. 6A, LNA (651) comprises the current gain block (610). The LNA
(651) further comprises an output load (621) comprising a
transistor pair (T63', T64') arranged in a stack configuration.
According to an embodiment of the present disclosure, transistors
(T63', T64') are NMOS transistors. According to embodiments of the
present disclosure, the output load (621) may comprise one or more
cascode transistors.
[0038] As described previously, the teachings of the present
disclosure provide methods and devices for supporting step-variable
gain for low Noise Figure (NF) in high gain states and high
linearity in low gain states. FIG. 7 shows an LNA (700) in
accordance with embodiments of the present disclosure, operating in
three different gain states: high gain, medium gain and low gain
states. The principle of operation of LNA (700) is similar to what
is described before with regards to the LNA (650) of FIG. 6A. LNA
(700) further comprises switches (S1, . . . , S6), states of which
will indicate what gain state is LNA (700) configured to operate
in. FIG. 7 shows three different signal paths (710, 711, 712) of an
input signal travelling from an input terminal (in) to an output
terminal (out). When LNA (700) is in the medium gain state,
switches (S1, S3) are closed and all other switches are open. The
input signal coming in from the input terminal (in) will travel
path (710) to output terminal (out). In other words, in the medium
gain state, transistors (T1, T2) are bypassed and the input signal
experience gain through a common gate configuration based on
transistors (T3, T4). Signal path (711) corresponds to the high
gain state. In such state, switches (S2, S6) are closed and all
other switches are open. As a result, the input signal experience
gain first by passing through transistors (T1, T2) being configured
in common source, and then by passing through transistors (T3, T4)
configured as common gate. When in the low gain state, switches
(S4, S5) are closed and all other switches are open. In this state,
which corresponds to signal path (712), all transistors are
bypassed and the input signal experiences practically no gain while
travelling from input terminal (in) to output terminal (out). The
person skilled in art will understand that switches (S2, S6) are
optional and mainly used for isolation purposes. In other words,
switches (S2) or (S6) are closed when their corresponding pair of
switches (S1, S3) or (S4, S5) are open. Moreover, embodiments with
only series switches and without switches (S2, S3, S4, S6) in
accordance with the present disclosure may be designed. According
to further embodiments of the present disclosure, the switch
network, may be configured according to desired isolation
requirements.
[0039] FIG. 8 shows an LNA (800) designed to operate in a first, a
second and a third gain state. The principle of operation of LNA
(800) is based on similar concept as to what described with regards
to LNA (700) of FIG. 7. LNA (800) comprises switches (S81, . . . ,
S86). In the first gain state, switches (S81, S83) are closed and
all other switches are open. As a result, transistors (T1, T2) are
bypassed and an input signal traveling from an input terminal (in)
to an output terminal (out) will experience a first gain state by
passing through transistors (T3, T4) which are configured in common
gate. In the second gain state, switches (S84, S86) are closed and
all other switches are open. As a result, transistors (T3, T4) are
bypassed and the input signal traveling from the input terminal to
the output terminal will experience a second gain state by passing
through transistors (T1, T2) which are configured in common source.
In the third gain state, switches (S81, S83, S84, S86) are closed
and switches (S82, S85) are open. As a results, all transistors
(T1, T2, T3, T4) are by passed. The first, the second and the third
gain states corresponds respectively to the signal paths (810, 811,
812) shown in dotted lines in FIG. 8.The common source and common
gate configurations as explained above may be used to support two
different gains depending on design requirements. The person
skilled in art will understand that switches (S82, S85) are
optional and mainly used for isolation purposes. In other words,
switches (S82) or (S85) are closed when their corresponding pair of
switches (S81, S83) or (S84, S86) are open. With reference to FIGS.
7-8, embodiments in accordance with the present disclosures may be
designed to support a number of one or more gain states using a
number of one or more switches. With reference to FIG. 8, the
person skilled in the art will appreciate that, there is only one
connection point between the current gain stage (including
transistors (T1, T2)) and the load section (including transistors
(T3, T4)). This allows a more modular approach compared to, for
example, the design as shown in FIG. 7, resulting in a simpler
layout configuration. By way of example, in a design comprising
several current gain stages and several loads, an easier layout
configuration is made possible as only one connection is required
to be made between each current gain stage and each load compared
to designs wherein more than one connection would be required to
connect each current gain stage to each corresponding load.
[0040] A number of embodiments of the invention have been
described. It is to be understood that various modifications may be
made without departing from the spirit and scope of the invention.
For example, some of the steps described above may be order
independent, and thus can be performed in an order different from
that described. Further, some of the steps described above may be
optional. Various activities described with respect to the methods
identified above can be executed in repetitive, serial, or parallel
fashion.
[0041] It is to be understood that the foregoing description is
intended to illustrate and not to limit the scope of the invention,
which is defined by the scope of the following claims, and that
other embodiments are within the scope of the claims. (Note that
the parenthetical labels for claim elements are for ease of
referring to such elements, and do not in themselves indicate a
particular required ordering or enumeration of elements; further,
such labels may be reused in dependent claims as references to
additional elements without being regarded as starting a
conflicting labeling sequence).
* * * * *