Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
2000-08-30
2002-04-02
Shingleton, Michael B (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S302000, C330S305000, C330S311000
Reexamination Certificate
active
06366166
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the field of low noise amplifier circuits (LNA) and, more specifically, to amplifiers used in radio frequency reception heads. The present invention more specifically applies to low noise amplifiers and to radio frequency reception heads intended for mobile telephony circuits likely to operate in two distinct frequency bands, for example, centered on 950-MHz and 1.85-GHz frequencies. Such mobile telephony systems are called double-band systems and the central frequencies associated with each band depend on the telecommunication standards. For example, for standards GSM and DCS, the reception bands (that transit through a head to which the present invention applies) are respectively included between 925-960 MHz and 1805-1880 MHz, with the transmission bands being respectively included between 880-915 MHz and 1710-1785 MHz. The use of double-band systems is linked to a need for increasing the capacity of mobile telephony networks.
BACKGROUND OF THE INVENTION
FIG. 1
very schematically shows a conventional example of a double-band type radio frequency reception head
1
. Head
1
receives a radio frequency signal RF that comes from a reception antenna (not shown) by transiting, possibly, through an antenna coupler and/or an isolation transformer (not shown). Most often, as will be seen hereafter, the radio frequency signal is of differential form. However, for simplification,
FIG. 1
will be discussed in relation with a non-differential operation.
Signal RF is sent onto two low noise amplifiers
2
,
3
(LNA
1
, LNA
2
), respectively associated with each central frequency of the system pass-bands. For example, amplifier
2
exhibits a maximum gain for a frequency on the order of 1850 MHz, while amplifier
3
exhibits a maximum gain for a frequency on the order of 950 MHz. Each amplifier
2
,
3
is associated, at its output, with a filter
4
,
5
(F
1
, F
2
) of band-pass type. Filters
4
and
5
are used to suppress the image frequencies of the respective central frequencies of the pass-bands. These filters are generally formed in so-called coplanar technology and are of surface wave type. In the above example, filter F
1
is centered on the 950-MHz frequency, while filter F
2
is centered on the 1850-MHz frequency. The respective outputs of filters
4
and
5
are sent onto first inputs of two multipliers
6
,
7
. The second respective inputs of multipliers
6
and
7
receive a frequency from a local oscillator OL
1
, OL
2
. The respective frequencies of local oscillators OL
1
and OL
2
are chosen so that, at the output of one of multipliers
6
and
7
, the central frequency of signal FI corresponds, whatever the channel, to the intermediary frequency chosen for the radio frequency head. According to applications, the frequency of output signal FI of head
1
is the central frequency of the channel, or another arbitrary low frequency (for example, on the order of some hundred MHz, or even less). In applications to mobile telephony, the width of each channel is 200 kHz.
Amplifiers
2
and
3
and multipliers
6
and
7
are controlled by signals, respectively CTRL and NCTRL, having the function of selecting one of the two parallel paths of the radio frequency head according to the band in which the received channel is located.
FIG. 2
still very schematically shows a second example of a radio frequency reception head
1
′. As in the example of
FIG. 1
, each frequency band is associated with a low noise amplifier, respectively
2
,
3
, the activation of which is obtained by a control signal, respectively CTRL and NCTRL. The essential difference between
FIG. 1 and 2
is that, in
FIG. 2
, an image frequency reject mixer
10
is used. Such a mixer includes two input multipliers
11
,
12
receiving, each, the signal coming from the operating amplifier
2
or
3
and the frequency provided by a local oscillator OL
1
or OL
2
, respectively phase-shifted by 90° for multiplier
11
and unshifted for multiplier
12
. The selection of the local oscillator OL
1
or OL
2
to be used is effected by means of a switch Ko controlled, for example, by one of signals CTRL or NCTRL to select the local oscillator adapted to the amplifier
2
or
3
that is used. The respective outputs of multipliers
11
or
12
are individually sent, via selectors, respectively K
1
and K
2
, onto phase-shifters by plus or minus 45°. Thus, multiplier
11
is associated with two phase-shifters
13
and
14
, respectively by +45° and by −45°, the respective inputs of which correspond to two output terminals of selector K
1
, the input of which is connected to the output of multiplier
11
. Similarly, multiplier
12
is associated with two phase-shifters
15
and
16
respectively by +45° and by −45°, the respective inputs of which are associated with two output terminals of selector K
2
, the input terminal of which is connected to the output of multiplier
12
. The output terminals of phase-shifters
13
and
14
are connected to a first input of an adder
17
while the output terminals of phase-shifters
15
and
16
are connected to a second input of this adder
17
, the output of adder
17
providing the signal at intermediary frequency FI. Of course, a single phase-shifter of each pair
13
,
14
or
15
,
16
is used according to the received radio frequency band. Further, the phase-shifters are used in opposition, that is, if the output of multiplier
11
is phase-shifted by +45°, the output of multiplier
12
is phase-shifted by −45°, and conversely. Selectors K
1
and K
2
are, for example, respectively controlled by signals CTRL and NCTRL to select the respective phase shifts to be brought according to the frequency of signal RF.
The operation of the double-band radio frequency heads such as illustrated in
FIGS. 1 and 2
is perfectly well known and will not be detailed any further. It should only be noted that image frequency reject mixer systems are described in many publications, for example “A 2.5 GHz BiCMOS image reject front end”, by M. D. Mc Donald, ISSCC93, paper TP94, pp. 144-145, “An improved Image Reject Mixer and a Vco fully integrated in a BiCMOS process”, by D. Pache, J. M. Fournier, G. Billot and P. Senn, in Proceed in Nomadic Microwave for Mobile Communications and Detection, Arcachon, November 1995, and “An improved 3 V 2 GHz BiCMOS Image Reject Mixer IC” by D. Pache, J. M. Fournier, G. Billot and P. Senn, in Proceedings of CICC, May 1995, USA, the respective contents of which are incorporated herein by reference.
FIG. 3
very schematically shows the upstream portion of a radio frequency reception head
1
,
1
′ such as illustrated in
FIGS. 1 and 2
, that is, the portion located upstream of amplifiers
2
,
3
. In the example of
FIG. 3
, the case where the low noise amplifiers receive differential signals has been shown, which is most often the case. As illustrated in
FIG. 3
, an antenna
20
intercepts the radio frequency signal. This antenna is associated with the primary winding
21
of a transformer
22
, the secondary winding of which has a midpoint, so that a first portion
23
a
provides signal RF while a second portion
23
b
provides inverted signal NRF. The midpoint of the secondary winding receives a voltage reference REF, for example the ground. Signals RF and NRF are each sent onto the two differential inputs of low noise amplifiers
2
and
3
. Each amplifier
2
,
3
, has, similarly, two differential outputs towards filters
4
and
5
(
FIG. 1
) or mixer
10
(FIG.
2
).
A disadvantage of conventional double-band radio frequency reception heads is that low noise amplifiers are particularly bulky. Accordingly, the use of two low noise amplifiers for each frequency of the double-band system adversely affects the system miniaturization, be it in terms of silicon surface for the integration of the radio frequency head, or in terms of number of input/output terminals, each frequency having its specific input. This in particular introduces two external matching networks. A
Jorgenson Lisa K.
Seed IP Law Group PLLC
Shingleton Michael B
STMicroelectronics S.A.
Tarleton E. Russell
LandOfFree
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