Phase correction circuit for transistor using high-frequency...

Details Phase correction circuit for transistor using high-frequency... Phase correction circuit for transistor using high-frequency...

2002-06-17

2003-08-05

Ton, My-Trang Nu (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

External effect

Temperature

Reexamination Certificate

active

06603343

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a phase correction circuit for a transistor using a high-frequency signal, which is used for a radio communication device, for example.
BACKGROUND OF THE INVENTION
It has been well known to those skilled in the art that a threshold voltage V
TH
of a gate of a transistor is increased by an increase in the temperature of the transistor. If the threshold voltage V
TH
has been increased, a high-level voltage of a control signal supplied to the gate needs to increase up to a value corresponding to the increased threshold voltage V
TH
, so that the transistor can work correctly. Otherwise, other circuits provided on the downstream side of the transistor and using an output signal of the transistor cannot work correctly.
In order to solve the problem, a temperature compensation circuit has been proposed so far. The circuit supplies a compensation voltage which increases together with the increase in temperature of the transistor, so that the transistor can work correctly, even if the high-level voltage of the control signal is fixed irrelevant to its temperature change.
FIG. 14
shows a depletion type n-channel field effect transistor
100
of which a gate is connected to not only a control signal line but also a temperature compensation circuit
10
. A threshold voltage V
TH
of the transistor
100
is −1.5V. A drain of the transistor
100
is supplied with a voltage Vcc. A source of the transistor
100
is connected to the ground. Also, the drain of the transistor
100
is connected to a high-frequency circuit
200
.
The temperature compensation circuit
10
functions as a potential dividing circuit. The circuit
10
has a load circuit
11
and a resistor
12
connected in series to the load circuit
11
. The joint P
1
between the load circuit
11
and the resistor
12
is connected to the gate of the transistor
100
. More particularly, the load circuit
11
has three diodes
11
a
,
11
b
and
11
c
, connected in series and supplied with a forward bias. A terminal
13
beside the load circuit
11
is supplied with Vg
1
=−1v. A terminal
14
beside the resistor
12
is supplied with Vg
2
=−5v. A resistance Rd of the load circuit
11
is increased by a temperature increase. This is caused by a well-known temperature characteristic of the diode being supplied with forward bias, i.e., each resistance of the forward biased diode
11
a
,
11
b
and
11
c
is increased by the temperature increase.
A potential of the joint P
1
, or a compensation voltage being supplied to the gate of the transistor
100
is increased by an increase in resistance Rd of the load circuit
11
with the temperature increase. An incremental ratio of the compensation voltage for the temperature increase is determined identically to that of the threshold V
TH
of the transistor
100
for the temperature increase. Therefore, the transistor
100
can work correctly, even if the high-level voltage control signal is not changed with the increase in temperature of the transistor
100
.
As described above, the temperature compensation circuit
10
can supply the compensation voltage increasing together with the increase in temperature of the transistor
100
to the gate of the transistor
100
. If the transistor
100
having the temperature compensation circuit
10
is used as a transistor for a high-frequency circuit, it causes a problem that a phase of output signal from the transistor
100
is shifted together with the increase in supply voltage, because a depletion capacitance increases together with the increase in supply voltage. If an amount of phase shift is increased, a following high-frequency circuit
200
can not work correctly.
As the phase correction circuit for a transistor using a high-frequency signal, several circuits have been proposed in various documents: a phase temperature compensation high frequency amplifier in JP A 03-258008, a semiconductor device and amplifier in JP A 11-74367, and a peaking circuit in JP A 01-137713, for example.
The phase temperature compensation high frequency amplifier in JP A 03-258008 has a circuit functioning as a phase correction circuit. The circuit has a varactor diode and a potential dividing circuit, adjusting a supply voltage of the varactor diode. The potential dividing circuit uses a positive thermistor having a resistance varying with its temperature. It is well known by those skilled in the art that the relationship of the capacitance of the varactor diode to the supply voltage is determined by a state of a p-n junction. That is, at the step junction, the depletion capacitance of the varactor diode changes in simple proportion to the square root of the supply voltage. In addition, at the graded junction, the depletion capacitance of the varactor diode changes in inverse proportion to the cube root of the supply voltage. On the contrary, the depletion capacitance of the transistor changes in simple proportion to the increase of its temperature. Therefore a compensated phase does not indicate any constant value in relation to its temperature change, or cannot have a linear relationship as described in JP A 03-258008. In addition, the semiconductor chip size becomes large because the amplifier needs to include not only the varactor diode but also a potential dividing circuit.
The semiconductor device and amplifier in JP A 11-74367 uses a diode that is inverse connected to another diode in an equivalent circuit of a transistor. The circuit supplies an inverse bias to the inverse connected diode. An electric potential of the inverse bias is set the same potential of the diode in the equivalent circuit. Therefore the capacitance changes of each of the diodes are canceled and therefore secondary unsymmetrical wave distortion can be removed. Nevertheless, this circuit cannot correct a phase shift caused by the increase in threshold voltage. In addition, JP A 11-74367 fails to disclose any circuit to correct a phase shift being caused by the temperature increase.
The peaking circuit in JP A 01-137713 can adjust a phase of an output signal from a transistor by means of a side-gate at a constant environment temperature. However, the circuit is not constructed to correct a phase shift caused by the increase in threshold voltage V
TH
due to the temperature increase. Also, in this third document, there is no description of a circuit to correct a phase shift caused by the temperature increase. In addition, the compensation circuit described in the third document is an only circuit to cancellation an influence from the side-gate.
SUMMARY OF THE INVENTION
Therefore, a purpose of the present invention is to provide a phase correction circuit to stabilize a phase of an output signal of the transistor, even if its gate potential is increased by a temperature compensation function, the temperature increase and the other reasons.
To this end, the phase correction circuit for the transistor using high-frequency signal, comprising: a) a circuit element connected in parallel to a gate of the transistor together with a control signal line, an impedance including a reactance component of the circuit element being changed by a potential difference between an input terminal and an output terminal of the circuit element; and b) a voltage control circuit for adjusting a supply voltage to the circuit element to decrease the reactance component in response to an increase in potential of the gate, wherein a total value of reactance components of the circuit element and the transistor is set to a predetermined value, so that another circuit using an output of the transistor can work correctly.
In another aspect of the present invention, the circuit element may be a diode of which a cathode is connected to the gate of the transistor. In this case, the voltage control circuit supplies predetermined reverse bias to the diode.
In another aspect of the present invention, the circuit element may be a diode of which a cathode is connected directly or indirectly to the gate of the transistor and a transmissi

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