JPH0374043B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a microwave mixer circuit using FETs (field effect transistors).

[Technical background of the invention and its problems]

Conventionally, diodes have been mainly used in microwave band mixer circuits, and the configuration of a diode mixer circuit is shown in FIG. In this diode mixer circuit, a signal from a signal input terminal 1 and a local oscillator signal from a local oscillator signal input terminal 2 are combined by a combiner 3 such as a directional coupler and applied to a mixer diode 4. An intermediate frequency signal component generated due to the nonlinear characteristic of current and voltage is extracted from an intermediate frequency (IF) output terminal 6 via a low-pass filter 5. That is, this diode mixer requires a synthesizer 3 for combining the signal and the local oscillator signal, making the circuit configuration complicated. Furthermore, since the combiner 3 is usually designed to weakly couple the local oscillator signal, it is necessary to increase the output of the local oscillator signal source, and there are disadvantages such as signal loss in the combiner 3, which degrades performance. It was hot. Furthermore, a matching circuit is usually required between the combiner 3 and the diode 4, but since the signal and the local signal have different frequencies, it is difficult to satisfy the optimal matching conditions at both frequencies, resulting in poor characteristics. It had the disadvantage of becoming.

On the other hand, with the improvement in performance of GaAsFET in recent years, FET
A microwave mixer circuit using a FET is used, and there is a gate mixer that applies the local oscillator signal to the gate of the FET, and a drain mixer that applies it to the drain. FIG. 2 is a circuit diagram of the gate mixer, and parts common to those in FIG. 1 are given the same numbers. 11 is a FET, and 12, 13, and 14 are a source, a gate, and a drain, respectively. That is, the source 12 is grounded, and the gate 13 is applied with a signal synthesized by a synthesizer and a local oscillation signal. The drain current is modulated by the local oscillation signal applied to the gate 13, and the signal is converted to an intermediate frequency due to nonlinearity such as the transconductance of the FET 11, and is taken out from the terminal 6 via the low-pass filter 5. . This gate mixer has the advantage of having a conversion gain, but because it requires a circuit to synthesize the signal and the local signal, it has the same drawbacks as the diode mixer described above.

On the other hand, the circuit configuration of the drain mixer is shown in FIG. In FIG. 3, the same numbers as those in FIG. 2 are given the same numbers. In addition, 37 and 38 are FETs, respectively.
35 and 36 are RF chokes, 32 to 34 are DC blocking capacitors, and 30 and 31 are matching circuits for signals and local signals, respectively. That is, the local oscillator signal input from the terminal 2 is transmitted to the drain 14.
Due to the nonlinearity of the capacitance Cgd between the gate and drain of the FET 11, the drain conductance gd, etc., the signal input from the terminal 1 and applied to the gate 13 is converted to an intermediate frequency, and the signal is applied to the drain 14.
is taken out from the terminal 6 via the low-pass filter 5. In other words, the drain mixer has the first
This has the advantage that there is no need for a synthesizer between the signal and the local oscillator signal as described in FIGS. However, all conventional FET mixers require a bias voltage to be applied to the drain and gate, and GaAsFETs in particular have the disadvantage of requiring two types of power supply, one positive for the drain and one negative for the gate.
In order to unify the FET bias from one power supply, a self-biasing resistor ( _RS ) and a high-frequency shorting capacitor ( _CS ) are sometimes connected in parallel between the source and ground, but this method requires a complicated circuit. As the number of interconnected wires increases, problems such as deterioration of high frequency characteristics and reliability arise.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks, and provides a microwave mixer that eliminates the need for a mixer for the signal and the local oscillation signal, operates without any bias power supply, and has excellent separation between the signal and the local oscillation signal. The purpose is to provide circuits.

[Summary of the invention]

The present invention provides a microwave mixer circuit having a configuration in which the source of the FET is grounded, a high frequency signal is applied to the gate, a local oscillation signal is applied to the drain, and an IF is output from the drain. This is a microwave mixer circuit characterized in that no bias voltage is applied.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a configuration diagram of the mixer circuit of the present invention,
44 is FET, 45, 46, 47 are each FET
44 sources, gates, and drains. FET
The source 45 of 44 is grounded, and a matching circuit 50 for the signal is connected between the gate 46 and the signal input terminal 41.
will be established. A signal input is applied from the signal input terminal 41 to the gate 46 via the matching circuit 50. On the other hand, the terminal 42 is a local oscillation signal input terminal, and the local oscillation signal is applied to the drain 47 via a bandpass filter 49 and a matching circuit 51 for the local oscillation signal. When a signal and a local oscillation signal are applied to the FET 44 in this way, an intermediate frequency component is generated due to the nonlinear effect of the FET 44 described below, and this intermediate frequency signal is passed from the drain 47 to the intermediate frequency pass filter 48.
It is taken out from the terminal 43 via. That is,
This mixer has a similar circuit configuration to the drain mixer shown in FIG. 3, but no bias is applied to the drain and gate of the FET. However, in the case of an operating condition in which a self-rectified current flows through the FET due to a local signal, a DC return circuit 55 is connected between an arbitrary terminal having the same DC potential as the drain 47 and the ground. Further, in order to make the gate and the source have the same potential, a chiyoke circuit 53 is connected between an arbitrary terminal having the same DC potential as the gate 46 and the ground.

The operating principle of this FET mixer will be explained below using Schottsley's gradient channel model. If the source, gate, and drain voltages of the source-grounded FET are V _S (=0), V _G , and V _D , respectively, the drain current I _D is divided into the non-saturation region (I _D = I _D1 ) and the saturated region (I _D = I _D2 ) and approximated as follows.

I _D1 = I _S [3V _D /U _O −2 {(V _D −V _G +V _B /U _O )) ^2/3 −(−V _G +V _B /U _O ) ^2/3 }] …(1) I _D2 = I _S [1-3-V _G +V _B /U _O +2 (-V _G +V _B /U _O ) ^2/3
] ...(2) However, I _S is the drain saturation current when V _G = V _B , V _B is the gate built-in voltage, V _p is the pinch-off voltage, and U _O = V _B + V _p . Also, I _D = I _D1
(V _D < U _O + V _G − V _B ), I _D = I _D2 (V _D > U _O + V _G − V _B ).

In Figure 5, V _B = 1V, V _p = 2.5V (U _O = 3.5V), I _S
= 0.1A, and the change in I _D with respect to V _D when V _G = 0 V and -2.5 V is shown. Note that when V _D <0, the direction of the drain current is reversed. Within the range of V _D > V _G −V _B , the V _D −I _D characteristic is not symmetrical with respect to V _D ;
This results in nonlinear characteristics as shown in FIG. Now, it is assumed that the DC bias voltage V _D0 and the local oscillator signal V _L = v _l sinω _l t are applied to the drain, but the DC bias voltage V _G0 and the signal V _S = v _S sinω _S t are applied to the gate. , if the drain current of only the second term in equation (1) related to mixer operation is I' _d , then I' _d = −2I _S /U _O ^2/3 (V _B +V _D0 −V _G0 +v _l sinω _l t-V _S Si
nω _S t ₎ ^2/3 …(3), and assuming that A=2I _S /U _O ^2/3 and V _X = V _B +V _D0 −V _G0 , I′ _d = _−A ( _V t−v _S sinω _S t) ^2/3 …(4) If I″ _d , which includes only the linear term of v _S , is extracted, I″ _d = 3/2A (V _X + v _l sinω _l t) ^{2/ 3} V _S sinω _S t…(5). _{( V _} ^_ _{_ _ _ _} The intermediate frequency component I _dif included in the current is That's what I find. As is clear from equation (6), V _B +V _D0 −
Within the range that satisfies V _G0 > 0, the smaller V _B +V _D0 −V _G0 becomes, the larger I _dif becomes, and the smaller the conversion loss becomes. That is, V _D0 is negative and V _G0 is positive, and the larger the absolute value of each, the larger I _dif , but in reality, V _B is as small as about 1 V, and V _D0 ≧0, V _G0 ≦0 Within the practical operating range, the conversion loss is smallest when the drain DC bias V _D0 and the gate DC bias V _G0 are both 0V. Moreover, this case has great advantages in terms of circuit configuration. In other words, this mixer circuit does not require a signal and local signal synthesis circuit,
Moreover, since the capacitance between the gate and drain of the FET is small, the leakage power of the local signal to the signal terminal is small, and since the FET does not require a DC bias voltage, it has the advantage of operating without any power supply.

〔Effect of the invention〕

As described above, according to the present invention, there is no need for a combining circuit for a signal and a local oscillator signal, thereby eliminating the disadvantages such as signal loss and increased local power generated by conventional diode mixers. Furthermore, it is possible to provide a microwave mixer circuit which has low leakage power of the local oscillator signal to the signal terminal and can be operated without any bias power supply.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional diode mixer circuit, Fig. 2 is a block diagram of a conventional FET gate mixer circuit, Fig. 3 is a block diagram of a conventional FET drain mixer circuit, and Fig. 4 is a block diagram of the FET drain mixer circuit of the present invention. FIG. 5 is a block diagram showing one embodiment of the circuit, and is a curve diagram showing an example of the drain voltage and current characteristics of the FET to explain the operation of the FET drain mixer circuit according to the present invention. 1,41...Signal input terminal, 2,42...Local signal input terminal, 6,43...IF output terminal, 11,44
...FET, 5, 29, 48, 49...Filter, 3
0, 31, 50, 51... matching circuit, 32, 33,
34...Capacitor, 35, 36, 53...RF chiyoke.

Claims (1)

[Claims] 1. In a microwave mixer circuit having a configuration in which a field effect transistor is connected to the source, a high frequency signal is applied to the gate of the field effect transistor, a local oscillation signal is applied to the drain of the field effect transistor, and an intermediate frequency signal is output from the drain, the field effect transistor A microwave mixer circuit characterized in that its drain and gate are not grounded to a bias power supply but are grounded through a part of a matching circuit.