JPH03204208A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To eliminate the need for a separate circuit by employing an FET having a side gate electrode as a nonlinear device, and supplying a converted signal to a gate electrode and a local oscillation signal to the side gate electrode. CONSTITUTION:The threshold voltage of a field effect transistor(FET) 1 is fluctuated depending on a voltage applied to an electrode (side gate electrode) 50 arranged near the gate electrode, but in such a case, the side gate effect is, in turn, utilized positively. That is, a local oscillating signal VOSC is supplied to the side gate electrode 50 to vary the threshold voltage Vth of the FET 1. The drain current of the FET is made intermittent by the local oscillating signal by setting a gate bias voltage Vb to be nearly (Vth1+Vth2)/2 (range of the change is (Vth1 to Vth2) to attain mixing. Thus, no separate circuit is required.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency conversion circuit (mixer) used in wireless communication or broadcasting systems.

[Conventional technology]

Conventionally, there are circuits of this type that utilize the nonlinear characteristics of FETs (field effect transistors). The basic circuit configuration is shown in FIGS. 3 and 4. Figure 3 shows a so-called gate type mixer, in which the signal to be converted (RF multiplied signal frequency f)
RF) vRF and local oscillation signal (intermediate frequency signal, frequency f
)v is applied to the gate of Fosc osc ET. On the other hand, FIG. 4 shows a drain type mixer in which the local oscillation signal V is applied to the drain side of the drain.

[Problem to be solved by the invention]

In the gate type mixer shown in Fig. 3, vl? F and voS
Since both are applied to the same electrode (gate electrode), an attached circuit is required to isolate both. In the case of a mixer, this separation is not easy because a signal with an extremely large amplitude is used as (1).

In particular, products used in the microwave band require complex circuits that are difficult to incorporate into ICs (integrated circuits), so measures such as complete isolation by forming an external circulator are required. becomes.

In the drain type mixer shown in Figure 4, VRF and ■
Although it is not necessary to separate the output signal O8C from the drain, this V and 0

A circuit that separates 0 and 0 is still required.

SC [Means for Solving the Problems] The present invention uses an FET as a nonlinear device in which a side gate electrode made of an ohmic electrode is arranged on the same semiconductor substrate near the gate electrode, A local oscillation signal is applied to the electrode.

[Effect]

In a FET, it is known that the threshold voltage varies as shown in FIG. 2 depending on the voltage V applied to an electrode (side gate electrode) placed near the gate electrode. This phenomenon can occur, for example, when FETs are
Suppression of this is a technical issue as it hinders high density when increasing the density, but here we will actively utilize this side gate effect on the contrary. That is, by applying the local oscillation signal SC to the side gate electrode, the threshold voltage vth of the FET is changed.

If this change range is set as Vthl to vth2, and the gate insulator pressure V is set to approximately (vthl+vth2)/2, the drain current of the FET will be interrupted and interrupted by the local oscillation signal, and the mixing operation will be controlled. will be carried out.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIG. 1 of the accompanying drawings.

FIG. 5A is a circuit diagram showing the configuration of the mixer of this embodiment. In the figure, the FETI has a side gate electrode 50 as described later, and a gate electrode (between the gate and source).
For the converted signal vRF (frequency fRP), for the side gate electrode 50 (between the side gate and source), the local oscillation signal V. The configuration is such that the s0 frequency (f) is applied to each SC. Reference numeral 2 indicates a matching circuit. If the converted signal vRP input to the gate electrode of FET1 is a signal with a very high frequency, the input signal will be reflected and will not flow into the FETI unless it is matched with the input impedance of the FETI. The matching circuit 2 is a circuit for this purpose.

Further, reference numeral 3 indicates an attenuator, and the local oscillation signal V
This prevents SC from being reflected and returning to the local oscillator. As mentioned above, the nonlinearity of FETI is brought out by using an extremely large power, for example, +10 dB for Se, as the local oscillation signal V.

If a high-power signal like this were to return to the local oscillator intact, the circuit could be destroyed.

Therefore, if a -3 dB attenuator 3 is inserted, for example, the round-trip attenuation will be -6 dB. This corresponds to "3" in VSWR (voltage standing wave ratio), which is 5 from the oscillator side.
It becomes quite close to 0Ω.

Further, reference numeral 4 indicates a filter. This is to extract only the frequency-converted signal from the drain output of FET 1, and if the mixer of this embodiment is used as a down converter, for example, a low-pass filter is used.

Further, the source of FET1 is grounded.

Here, the local oscillation signal vO8e is applied to the side gate electrode 50.
The bias voltage Vb between the gate and source is set to approximately (vthi+vth2)/2, assuming that the threshold voltage change range of the FETI due to the application of is from ■th□ to vth2. Then, ■vt depending on the level of O8e
When v b <vth due to a change in h, the FET
I is in a cutoff state, and when v b >V, it is in a conduction state. In other words, the drain current of the FETI is turned off by the local h oscillation signal V, so that a mixing operation can be performed. Moreover, since the side gate electrode 50 to which the local oscillation signal V SC is applied is an electrode independent from the others, no separation circuit is required at all.

FIG. 1(b) shows the structure of the FETI. The figure shows only the planar arrangement of each electrode, wiring pattern, etc., and the interstation insulating film and the like are omitted. Code 10 is Ga
A semi-insulating substrate made of As is shown, and on the substrate 10 are long electrodes (gate electrode 20, source electrode, etc.) extending in the gate width direction.
A wiring layer 30, a drain electrode/wiring layer 40, and a side gate electrode 50 are arranged.

The FET of this embodiment is a low-noise oriented microwave FET, and in order to minimize the noise figure, the gate electrode 20 is connected to the gate input terminal ( (pad) 22.

Correspondingly, the side gate electrodes are also distributed and arranged at a total of five locations, including each of the feed point portions and both ends. Each side gate electrode 50a to 50e is made of a metal electrode that makes ohmic contact with an n+ region formed on the substrate 1o, and has an air bridge structure in which the gate electrode straddles the side gate electrode at the intersection with the gate electrode 2o. By doing so, the gate capacitance is reduced.

The gate electrode 20 forms a Schottky junction with the active layer 11 indicated by the chain line in the figure.

On the other hand, the source and drain electrodes are formed in ohmic contact with n+ regions formed on both sides of the gate electrode 20. Therefore, these source and drain electrodes are formed by the lower wiring layer and are connected to the upper layer terminals 31 and 41 via contact holes. Note that the drain wiring layer in the portion of the side gate electrode 50 that intersects with the lead wiring 51 and the source wiring layer in the portion that intersects with the drain wiring layer are each formed of an upper wiring layer.

The gate, drain, and side gate terminals (pads) are arranged in dimensions that allow them to be blown with, for example, a microwave wafer blower manufactured by Cascade Microtic, making it easy to perform the modeling necessary for circuit design using a network analyzer, etc. This is possible up to a maximum of 26.5 GHz.

The width W of the lead wiring to the drain is such that its characteristic impedance is 5oΩ (100μm thick Ga
When the substrate 1o is made of As, the thickness is approximately 70 μm), making it difficult to match the measurement system. Also, source terminal 31
is connected to ground.

Here, the difference in electrical length between the side gate input terminal 52, each side gate electrode 50a to 50e, and the lead wiring 51 connecting these, from each side gate electrode 50a to 50e to the side gate input terminal 52 is as follows. It is formed so that it has a sufficiently large size that can be ignored with respect to one-fourth of the wavelength at the frequency used as the side gate input signal. In this embodiment, the side gate electrodes 5o are arranged symmetrically with respect to a center line that bisects the gate electrode 20 at the center in the gate width direction, and the side gate electrodes 50a and 5o
The electrical lengths of terminals e, 50b and 50d to the side gate input terminal 52 are completely equal.

This electrical length is the largest for the side gate electrodes 50a and 50e at both ends, and the smallest for the side gate electrode 50c in the center, but the difference between these is 10GH in this embodiment.
The wavelength is set to be less than 1/10 (about 200 μm) of the 1/4 wavelength of the z signal.

Thereby, the phase difference when the microwave signal applied to the side gate input terminal 52 reaches each side gate electrode 50a to 50e can be ignored. Therefore, it is possible to apply microwaves as a local oscillation signal to the side gate electrode 5o.

〔Effect of the invention〕

As explained above, the present invention uses an FET having a side gate electrode as a nonlinear device.
This has the effect of configuring a frequency conversion circuit that does not require a separation circuit.

[Brief explanation of drawings]

FIG. 1(a) is a circuit diagram of a mixer showing an embodiment of the present invention, FIG. 1(b) is a plan view showing an FET used therein, FIG. 2 is a diagram showing the side gate effect, FIG. FIG. 4 is a diagram showing a conventional example. DESCRIPTION OF SYMBOLS 1... FET, 10... Substrate, 20... Gate electrode, 50... Side gate electrode.

Claims (1)

[Claims] In a frequency conversion circuit using an FET as a nonlinear device, an FET is used in which a side gate electrode made of an ohmic electrode is placed on the same semiconductor substrate near the gate electrode, and the signal to be converted is placed on the gate electrode, and the side gate electrode is placed on the same semiconductor substrate near the gate electrode. Frequency conversion circuit that applies local oscillation signals.