JPH09130149A - Mixer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the local leak by using about half number of elements by turning on and off the bypass capacitance connected to the source of an AC amplifier via a 2nd FET which has a switching operation. SOLUTION: A mixer circuit turns on and off the bypass capacitance connected to the source of an AC amplifier consisting of a depletion type FET operating at a low current level by means of a 2nd FET having a switching operation. Then the mixer circuit eliminates the local leak occurring via the parasitic capacitance Cp by the local signal supplied from the gate of the amplifier via the capacitance Ccom. The local leak is not converted into a current signal as long as the gate potential is moved in an in-phase by an extent equal to the movement of a source electrode caused by a local leak signal. Thus the local leak is never outputted. In such a constitution, a mixer that is suitably applied to the mobile communication for suppression of the local leak is obtained by using a small number of elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixer circuit, and to realize a mixer having a mechanism for suppressing a local signal with a small circuit scale.

[0002]

2. Description of the Related Art With the spread of mobile communication, studies on integration of high-frequency RF circuits such as low-noise amplifiers, power amplifiers and mixers have been actively conducted. Among them, the transmission mixer is required to have high conversion gain, linearity, etc., and from the viewpoint of suppressing unnecessary radiation, it is strongly desired to reduce the amount of local signal leaking from the RF terminal and the amount of local leak. It is rare. Conventionally, Gilbert type multipliers have often been used to meet such demands. FIG. 6 shows an example of a transmission integrated circuit when a Gilbert-type multiplier is applied. This circuit consists of a transmitter mixer body and a local amplifier. Focusing on the mixer section, the Gilbert mixer has a differential pair 1 (Q8, Q9), a differential pair 2 (Q4, Q5), a differential pair 3 (Q6,
It consists of three differential pairs of Q7). An IF (intermediate frequency) signal is input to one gate of the differential pair 1 to convert the signal from a voltage to a differential current. Reverse phase differential local signals are applied to the differential pairs 2 and 3 to operate as current switches for frequency conversion. The local signal leaks to the RF output terminal via the gate-drain capacitance of each FET. However, Q4
The local signal leaking from Q6 and the local signal leaking from Q6 have opposite phases, so they cancel each other out, and as a result, the local leak can be removed. In the example of FIG. 6, the output is Q4,
I take out the single-phase output on the drain terminal side of Q6,
Even if it is taken out from the drain terminals of Q5 and Q7 and the differential output is used, the local leak can be eliminated for the same reason as in the case of the single phase. Local leakage can be attenuated by about 20 dB with this method. As described above, the Gilbert-type multiplier is an optimum circuit for suppressing the local leak.

[0003]

However, as is apparent from FIG. 6, the transmission mixer using the Gilbert type multiplier has a large number of elements. In order to suppress the local leak by using the Gilbert type multiplier, a differential local signal having a phase difference of 180 degrees is required, and the local amplifier also needs to be configured by a differential circuit. As described above, the transmission mixer using the Gilbert-type multiplier has a problem that it is difficult to downsize the integrated circuit and power consumption increases. In order to reduce the size and power consumption, it is strongly desired to realize the local leak suppression by using a smaller scale circuit.

[0004]

Considering the factors that increase the number of elements when a Gilbert-type multiplier is used, it is understood that the circuit is operating differentially. If the local amplifier could also be operated in a single phase, the number of elements would be halved. When the Gilbert-type multiplier is used, the local signal is canceled by combining signals of opposite phases. If it is possible to cancel the local signal between the single-phase signals, it is possible to expect a significant reduction in the number of elements. According to the present invention, the bypass capacitor connected to the source of the AC amplifier composed of the FET is turned on and off by the second FET that operates as a switch, and a local leak that leaks through the odd capacitance is injected from the gate of the amplifier. All circuits operate in single phase. The embodiment will be specifically described below.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described with reference to FIG. In the mixer circuit of the present invention, the bypass capacitance Cb connected to the source of the AC amplifier constituted by the constant current driven depletion type FET is turned on and off by the second FET which operates as a switch, and the local leakage leaks through the odd capacitance Cp. The leak is canceled by the local signal injected from the gate of the amplifier through the capacitance Ccom.
If the gate potential is moved to the same phase as the source potential is moved by the local leak signal, the local leak is not converted into a current signal and is not output.

The present embodiment will be described in more detail. If the local signal is ideally a square wave with a duty of 50%, the voltage gain of the amplifier when it is turned on is Av, and the gain when it is turned off is 0. The converted voltage gain in this case is Av / pi by a simple calculation. Here, pi represents the pi. Since the connection with the bypass capacitor is turned on and off,
The DC bias current is never turned on or off. Therefore, if an ideal switch with no odd capacitance is used, no local leak will occur from this mixer. However, since the strange capacitance Cp is present, the source potential of the FET1 is modulated and a local leak occurs. In order to cancel this, a local signal of the same phase and same amplitude is applied to the gate via the capacitor Ccom. The phase and amplitude of the signal applied to the gate is the capacitance Ccom
Therefore, these element values need to be optimized because they are affected by the resistance R1. The easiest is to select Ccom to be the same value as Cp and match R1 to the source impedance of FET1. According to the present invention, it is possible to realize a mixer suitable for application to mobile communication or the like that suppresses local leak with a small number of elements.

A second embodiment of the present invention will be described with reference to FIG. The present embodiment relates to a transmission integrated mixer that is a more specific version of the first embodiment. Although a single FET is used as the amplifier in FIG. 2, it is composed of two stages of cascode-connected FETs for improving the gain. The capacitor Ccom in FIG. 2 is realized by connecting the source and drain of the FET in FIG. FET4 size (gate width)
Is an appropriate value of 1/2 of FET3. R4 and R5 are F
This is for setting the gate DC bias of each ET to the ground level, and has a sufficiently high impedance, for example, a value of 3 kohm or more. Although the amplifier is driven by the constant current source I1 in FIG. 2, it is replaced with the resistor R1 in FIG. 1 in order to correspond to the low voltage operation. Of course, application of a constant current source composed of an FET does not go against the gist of the present invention. Further, if the impedance of the gate is made the same as the impedance of the source, the input voltage applied to the gate is lowered. Therefore, a series resonant circuit is provided in series with the resistance R3 for impedance adjustment, and the impedance is reduced only for the local signal. The impedance of the gate was set to be high with respect to the input signal. In this embodiment, a matching circuit for local signals is also provided, and the ground terminal also serves as the bypass capacitance terminal. The output matching circuit of this embodiment is composed of L1, L2, C1, C2 and R2. C
Reference numerals 1 and R2 are for relaxing the high output impedance of the cascode connection circuit and facilitating matching. According to the present invention, it is possible to realize a mixer suitable for application to mobile communication or the like that suppresses local leak with a small number of elements.

A third embodiment of the present invention will be described with reference to FIG. Here, a differential amplifier composed of FET1 and FET2 is applied to the amplifier, and the source coupling of the two FETs is switched by the FET3 to realize frequency conversion. Here, replacing the FET 2 with a cascode circuit from the viewpoint of improving the gain does not go against the gist of the present invention. A local signal is input to the gate of the FET2 through the FET4 that operates as a capacitance in order to cancel the local leak that is mixed through the parasitic capacitance of the FET3. FET
The resistor R3 is connected to the gate terminal so that the impedance of the second gate terminal becomes the same as the source impedance. In the second embodiment, since the local signal for canceling the local leak and the IF signal are applied to the gate of the same FET, the impedance element added to the gate needs to have frequency characteristics. Is input to the gate of FET1 and the local signal for canceling the local leak is input to the gate of FET2. Therefore, it is not necessary to have frequency characteristics, and only R3 can be used. However, since the differential circuit is used, the current consumption is almost double that of the single-phase circuit, but one series resonant circuit can be omitted as compared with the second embodiment.

FIG. 4 shows a fourth embodiment of the present invention. In this embodiment, a differential signal is taken out as an RF output. Since an output signal is transmitted from the drains of the FET1 and FET2, a local signal for canceling the local leak is applied to the gates of both FETs. At the gate terminal of the FET1 to which the IF signal is also input, a series resonance circuit is provided in series with the resistance R4 for impedance adjustment in the same manner as in the second embodiment, and the impedance is reduced only for the local signal. The gate impedance was set to be high for signals. According to the present embodiment, it is possible to realize a mixer circuit that is small but can obtain a differential output.

FIG. 5 shows a fifth embodiment of the present invention. This embodiment relates to an integrated transmission mixer in which a local amplifier is added to the second embodiment. The input matching circuit of the local amplifier is composed of C6, L6, L7,
A cascode circuit composed of FETs 5 and 6 is applied to the amplifier main body from the viewpoint of gain improvement, and an output matching circuit is C4 and C.
5, L4, L5 and R6. By adding a local amplifier, the mixer can be driven with a smaller local signal. As a result, it is possible to reduce local leakage outside the integrated circuit, that is, on the mounting substrate. This embodiment corresponds to the conventional transmission mixer of FIG. 6, but the number of constituent elements is reduced by about half. In the above embodiment, the n-type dip region type FET has been described.
The present invention does not limit the types of devices, and these can be realized by enhancement type MOSFETs and p-type FETs. Furthermore, bipolar transistors can be applied to amplifiers and FETs can be applied to switches. is there.

[0011]

According to the present invention, it is possible to realize a transmission mixer circuit suitable for mobile communication that can suppress local leakage with about half the number of elements as compared with the conventional Gilbert-type mixer circuit. The local leak is about 10 dB to 15 with this method.
It has been confirmed by simulation that attenuation by dB is possible, and it is possible to realize sufficiently practical characteristics although the performance is slightly lower than that of the Gilbert mixer.

[Brief description of the drawings]

FIG. 1 is a second embodiment of the present invention.

FIG. 2 is a first embodiment of the present invention.

FIG. 3 is a third embodiment of the present invention.

FIG. 4 is a fourth embodiment of the present invention.

FIG. 5 is a fifth embodiment of the present invention.

FIG. 6 shows a Gilbert mixer as a conventional example.

[Explanation of symbols]

FETn ... Field effect transistor, SW1 ... Switch (field effect transistor), I1 ... Current source,
Ln ... inductor, Cn ... capacitance, Rn ... resistance.

Claims (6)

[Claims] 1. A source-grounded or emitter-grounded first type
The first FET element is inserted between the source or emitter electrode of the AC amplifier and the first capacitance for bypassing, the source or drain is connected to the capacitance, and the remaining drain or source is the source of the first AC amplifier or A mixer circuit which is connected to an emitter electrode, applies a local signal to a gate of a first FET, and applies the local signal to an input terminal of a first AC amplifier via a first impedance element. 2. The mixer circuit according to claim 1, wherein the input impedance of the first AC amplifier is set to the second impedance.
A mixer circuit characterized in that the impedance element is substantially reduced by connecting the impedance element to an input terminal. 3. The mixer circuit according to claim 2, wherein the impedance of the second impedance element is low for a local signal and high for an input signal. . 4. The integrated mixer circuit according to claim 1, wherein a single-phase local amplifier is integrated on the same chip as the mixer circuit. 5. A common source or emitter of a first differential pair composed of a first FET or bipolar transistor and a second FET or bipolar transistor is divided, and a third FET element is provided between two electrodes. The inserted source or drain is connected to one source or emitter, the remaining drain or source is connected to the remaining source or emitter electrode, the local signal is applied to the gate of the third FET, and the local signal is applied to the first Through the impedance element, the input signal is applied to the gate or base terminal of the second FET or bipolar transistor, the input signal is applied to the gate or base terminal of the first FET or bipolar transistor, and the output signal is applied to the drain of the second FET or bipolar transistor. Or collector Mixer circuits, characterized in that retrieving al. 6. A common source or emitter of a first differential pair composed of a first FET or bipolar transistor and a second FET or bipolar transistor is divided, and a third FET element is provided between two electrodes. The inserted source or drain is connected to one source or emitter, the remaining drain or source is connected to the remaining source or emitter electrode, the local signal is applied to the gate of the third FET, and the local signal is applied to the first The input signal is applied to the gate or base terminal of the second FET or bipolar transistor via the impedance element, and the same local signal is applied to the gate or base terminal of the first FET or bipolar transistor via the second impedance element. First FE
In addition to the gate or base terminal of the T or bipolar transistor, a third impedance element whose impedance is low for a local signal and high for an input signal is connected to the gate or base terminal of the first FET or bipolar transistor. A mixer circuit characterized in that it is connected between ground terminals and outputs an output signal from the drain or collector of the first and second FETs or bipolar transistors.