Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Superconductive device
Reexamination Certificate
1999-03-18
2001-12-11
Lam, Tuan T. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Superconductive device
C327S359000, C327S103000
Reexamination Certificate
active
06329865
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to transconductance cells, in particular, to linearized transconductance cells for use in electronic circuits.
A transconductance cell is an electronic building block used to build more complex electronic circuits. It is widely used in RF circuits such as low noise amplifiers and Gilbert cell mixers.
The transconductance cell performs the function of converting a voltage input into a current output. The characteristics of a desirable transconductance cell are high bandwidth, low noise, low power consumption, high output impedance, low distortion and good common mode rejection.
FIG. 1
shows a schematic diagram of a prior art transconductance cell
20
. Other parts of the RF circuit (e.g., the Gilbert cell mixer) to which the transconductance cell
20
is connected are not shown. The prior art transconductance cell
20
for RF applications includes a first bipolar transistor
22
, a second bipolar transistor
32
, a first inductor
24
, a second inductor
30
, a resistor
26
and a capacitor
34
. A voltage input
21
is coupled to the base of the first transistor
22
. The collector of the first transistor
22
is coupled to another part of the circuit. The emitter of the first transistor
22
is coupled to one end of the first inductor
24
. The opposing end of the first inductor
24
is coupled to one end of the second inductor
30
. One end of the resistor
26
is coupled to a node between the first and second inductors
24
and
30
. The other end of the resistor
26
is coupled to a node
28
which may be a ground.
The opposing end of the second inductor
30
is coupled to the emitter of the second transistor
32
. The collector of the second transistor is coupled to another part of the circuit. The base of the second transistor
32
is coupled to the capacitor
34
and is biased at a constant voltage.
In operation, a bias voltage is applied to the transconductance cell
20
at the bases and the collectors of the first and second transistors
22
and
32
to bias the first and second transistors
22
and
32
for operation. In response to the bias voltage, DC currents flow through the first and second transistors
22
and
32
and exit through the resistor
26
. The bias voltage typically ranges between 2.7 volts and 5.5 volts for RF circuits. Much of the bias voltage is dropped across the resistor
26
which is designed to have high impedance, as explained below. The resistor
26
also can be implemented as a transistor which also cause a voltage drop.
Once the bias voltage has been applied, the voltage input
21
is applied to the base of the first transistor
22
to output a signal from the emitter of the first transistor
22
. The signal travels through the first and second inductors
24
and
30
and is output from the collector of the second transistor
32
to another part of the circuit. The signal output by the first transistor
22
may be directed from the first inductor
24
to the second inductor
30
without significant signal dissipation through the resistor
26
by using a resistor that has a high impedance value as the resistor
26
.
One problem associated with the prior art transconductance cell
20
is that this requisite high impedance of the resistor
26
makes it difficult to operate the circuit at a low voltage.
Another problem associated the prior art transconductance cell
20
that the noise factor (NF) and the third-order input intercept point (IIP
3
) are degraded due to signal loss in the resistor
26
. The noise contribution of the resistor
26
lowers the NF as well.
SUMMARY OF THE INVENTION
In one aspect, the invention features a linearized transconductance cell. The invention includes a first transistor having a control terminal and first and second terminals; a second transistor having a control terminal and first and second terminals, wherein a signal is output from the second terminal of the second transistor in response to an input voltage applied to the control terminal of the first transistor; a linear element coupled between the first terminal of the first transistor and the first terminal of the second transistor; and a tank circuit coupled between a reference voltage and a node between the linear element and the first terminal of the second transistor.
In another aspect, the invention features an electronic circuit including a transconductance cell. The transconductance cell includes a first transistor having a control terminal and first and second terminals; a second transistor having a control terminal and first and second terminals, wherein a signal is output from the second terminal of the second transistor in response to an input voltage applied to the control terminal of the first transistor; a linear element having first and second ends coupled between the first terminal of the first transistor and the first terminal of the second transistor; and a tank circuit having a first end coupled to a reference voltage and a second end coupled to a node between the linear element and the first terminal of the second transistor.
In another aspect, the invention features a transconductance cell having a single-ended input. The invention includes a first transistor having a control terminal and first and second terminals; a second transistor having a control terminal and first and second terminals, wherein a current flows between the first and second terminals of the second transistor in response to an input voltage applied to the control terminal of the first transistor; a first linear element having first and second ends, the first end coupled to the first terminal of the first transistor; a second linear element having first and second ends coupled between the second end of the first linear element and the first terminal of the second transistor; and a tank circuit coupled between a reference voltage and a node between the first and second linear elements.
In another aspect, the invention features a transconductance cell having a single-ended input; a first transistor having a control terminal and first and second terminals; a second transistor having a control terminal and first and second terminals, where a current flows between the first and second terminals of the second transistor in response to an input voltage applied to the control terminal of the first transistor; a linear element having first and second ends coupled between the first terminal of the first transistor and the first terminal of the second transistor; and an inductor coupled between a reference voltage and a node between the linear element and the first terminal of the second transistor.
Among the advantages of the invention are that the invention: (1) virtually eliminates consumption of the bias voltage and significantly improves the headroom; (2) significantly improves the noise factor (NF) since an inductor, a noiseless device, is used rather than a resistor; (3) significantly improves the third-order input intercept point (IIP3) when compared to a standard differential pair; and (4) allows for the tuned transfer characteristic.
For fuller understanding of the nature and further advantages of the invention, reference should be made to the detailed description taken in conjunction with the accompanying drawings.
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Hageraats Johannes J. E. M.
Shana'a Osama
Fish & Richardson P.C.
Lam Tuan T.
Maxim Integrated Products Inc.
Nguyen Hiep
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