Miscellaneous active electrical nonlinear devices – circuits – and – Specific input to output function – Combining of plural signals
Reexamination Certificate
1998-01-07
2001-04-03
Wells, Kenneth B. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific input to output function
Combining of plural signals
C327S356000, C455S333000
Reexamination Certificate
active
06211718
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to mixer circuits and in particular to mixer circuits having a single-ended input and a differential output.
RF mixers are the key blocks of modern radio systems and their parameters determine the main characteristics of the system in which they are used. The most common mixer circuit configurations are those of the Gilbert cell and the Micromixer, shown in
FIGS. 1 and 2
respectively.
Each of these mixer circuits receives at its input terminal a single-ended rf input signal and provides at its output a differential signal being the input signal first amplified and subsequently mixed with a signal from a local oscillator. Both of these circuits are easily implemented in IC form and are commonly used in mobile telephones and the like. However, mixers constructed using these circuit configurations exhibit poor noise properties. They also require a supply voltage of 2.7 V or more because each has three transistors in series between supply and ground. This can make them unsuitable for low voltage applications.
Referring to
FIG. 1
, Gilbert cell circuit
100
receives a single-ended input voltage signal at terminal
130
and a differential local oscillator voltage signal at terminals
140
and
141
. Transistors
101
,
102
, resistors
110
,
111
and current source
115
form a differential transconductance amplifier
160
whilst transistors
103
-
106
form a mixer core
150
. An increasing input voltage at terminal
130
will cause an increasing signal current to flow from the collector terminal of transistor
101
. Current source
115
and resistors
110
,
111
ensure that a complementary decreasing current will flow from the collector electrode of transistor
102
. These current signals will be balanced if current source
115
is implemented as a constant current source.
Mixer core
150
receives differential local oscillator signals on terminals
140
,
141
. When the voltage on terminal
140
is positive, the voltage on terminal
141
will be negative causing transistors
104
and
105
to be switched on and transistors
103
and
106
to be switched off. The collector current of transistor
101
will therefore be routed to output electrode
121
whilst the collector current of transistor
102
will be routed to output terminal
120
. The collector currents of transistors
101
,
102
will be switched to the opposite output terminal
120
,
121
when terminal
141
receives a higher voltage than terminal
140
.
The poor noise properties of this mixer configuration are due largely to the thermal noise of resistors
110
and
111
which produce noise directly in the main current paths. Current source
115
will also introduce noise into the output signal, because it experiences quite large voltage swings across its input and output terminals. A significant amount of noise will appear at output terminals
120
,
121
as a result of transistors
101
and
102
having their base resistances in series.
The micromixer circuit
200
of
FIG. 2
receives a single-ended input signal at input terminal
230
and differential local oscillator signals at terminals
240
and
241
. Transistors
201
-
203
and resistors
210
-
212
form a transconductance amplifier
260
whilst transistors
204
-
207
form a mixer core
250
.
An increase in voltage at input terminal
230
will cause increased current to flow from the collector electrode of transistor
202
and a decreased current to flow from the collector of transistor
203
. The circuit therefore acts as a transconductance amplifier having a single-ended input and a differential output. The output from amplifier
260
is provided on the collector electrodes of transistors
202
and
203
, as a differential current signal, to mixer core
250
.
Mixer core
250
functions in the same manner as mixer core
150
of the
FIG. 1
mixer circuit described above.
Micromixer circuits have very linear characteristics and large dynamic range at radio frequencies but, due to the large number of resistors used in the main current paths, have even worse noise properties than Gilbert cell circuits. There exists a need for a mixer circuit with improved noise properties and low voltage supply requirements.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a mixer circuit arrangement comprising a mixer core and a single-ended amplifier stage, in which the mixer core is arranged to receive a single-ended output signal of the amplifier stage on a first main input and to provide a differential output signal in response thereto.
In accordance with another aspect of the present invention there is provided a mixer circuit arrangement for providing differential output signals in response to an input signal applied thereto, comprising a mixer core having first and second current signal inputs and first and second local oscillator inputs, a single-ended amplifier stage for applying a current signal to said first signal input of said mixer core in response to said input signal, and bias means having a low ac impedance for applying a bias current to said second signal input of said mixer core.
REFERENCES:
patent: 4667342 (1987-05-01), Lindenmeier et al.
patent: 5521545 (1996-05-01), Terry et al.
patent: 5825231 (1998-10-01), Chevallier et al.
patent: 0 584 870 A1 (1994-03-01), None
patent: 0 726 646 A1 (1996-08-01), None
patent: 2 262 403 (1993-06-01), None
patent: 2 299 230 (1996-09-01), None
patent: 96/23365 (1996-08-01), None
Kirschstein et al.
Motel Semiconductor Limited
Wells Kenneth B.
LandOfFree
Low voltage double balanced mixer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Low voltage double balanced mixer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Low voltage double balanced mixer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2496209