Multiple-Band Mixer Circuit

This invention relates to a multiple-band mixer circuit for use in an LNB (Low Noise Blockdown Converter) in the outdoor unit of a satellite broadcast receiving station, which circuit is capable of receiving multiple bands of broadcast wave.

The conventional two-band mixer circuit contains two independent mixer circuit blocks to receive two bands, that is, the first and the second bands. To select either of the two bands, a selection circuit is connected to the two mixer circuit blocks, thereby allowing either of the mixer circuit blocks to operate. Two monitor circuits are connected separately to the two mixer circuit blocks, respectively, to check for the operation of the mixer circuit blocks. As a result, the two-band mixer circuit becomes large in size, thereby does not meeting the increasing demand in smaller components for a two-band mixer circuit-containing satellite broadcast receiving system.

In view of the above conventional problem, an object of the present invention is to provide a multiple-band mixer circuit having a monitor circuit which checks for the operating state of a plurality of mixer circuit blocks and is shared by the plurality of the mixer circuit blocks.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given below. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

To achieve the above object, according to an embodiment of the present invention, a multiple-band mixer circuit comprises at least two mixer circuit blocks, a selection circuit for selecting one of the mixer circuit blocks, and a monitor circuit provided for common use by the at least two mixer circuit blocks to monitor the operation state of the mixer circuit block selected by the selection circuit.

The present invention will become more fully understood from the detailed description given below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:

FIG. 1 is a circuit diagram of the two-band mixer circuit of an embodiment of the present invention.

The two-band mixer circuit of an embodiment of the invention is described with reference to the attached drawings. It should be noted that the present invention is not limited to a mixer circuit for two bands, the invention being applicable to more than two-band mixer circuits.

Referring to the figure, the two-band mixer circuit comprises a mixer circuit block M1 for a first band, a mixer circuit block M2 for a second band and a selection circuit block S for selecting the mixer circuit block M1 or M2. When the circuit has received a signal, the received signal and a local signal are supplied to the appropriate mixer circuit block M1 or M2. Specifically, when the first band has been received, the first band signal and a local signal are inputted to the terminal T1 of the band mixer circuit block M1 and converted to an IF signal by a mixer diode D.sub.11. The IF signal from the band mixer circuit block M1 is selected by the selection circuit block S and outputted to a terminal T3. When the second band has been received, the second band signal and a local signal are inputted to the terminal T2 of the band mixer circuit block M2 and converted to an IF signal by a mixer diode D.sub.21. The IF signal from the band mixer circuit block, M2 is then selected by the selection circuit block S and outputted to the terminal T3.

An appropriate band mixer circuit block M1 or M2 is selected by the line voltage supplied from a local oscillator selectively to either the terminal B1 or B2 of the selection circuit block S. The local oscillator supplies power only to the mixer circuit block appropriate for a received band, so that the mixer circuit block appropriate for the received band alone is operated. Voltage is applied selectively to either the terminal B1 or B2 of the selection circuit block S thereby connecting only the necessary mixer circuit block alone, with the selection circuit block S and preventing the influence by the mixer circuit block which is not operated. In the two-band mixer circuit of the present invention, a circuit comprising a resistor R.sub.11 and a capacitor C.sub.11 monitors the diode current of the band mixer circuit block M1 or M2. It is possible to check the mixer circuit block M1 or M2 for normal operation by measuring the voltage at the terminal TP of the monitor circuit.

According to the present invention, since the local oscillator supplies power only to the mixer circuit block appropriate for the band received, the two mixer circuit blocks will never operate simultaneously.

According to the present invention, only one parallel circuit comprising the resistor R.sub.11 and the capacitor C.sub.11 is connected as a monitor circuit to the two band mixer circuit blocks M1 and M2. The diode current for each band is led through a reactance L.sub.15 or L.sub.25 to the parallel circuit. Therefore, diode current of either mixer circuit block can be measured at one monitor terminal TP.

In the two-band mixer circuit of the present invention, the diode current of the mixer circuit block M1 or M2 flows through the reactance L.sub.15 or L.sub.25 to the resistor R.sub.11. When a local signal is supplied to the terminal T2 of the mixer circuit block M2, for instance, the diode current flows through L.sub.21, D.sub.21, L.sub.23, L.sub.25 and R.sub.11. At this time, the monitor circuit is linked via the reactance L.sub.15 with the other mixer circuit block M1, but the circuit is not influenced by the mixer circuit block M1 as direct current is blocked by a coupling capacitor C.sub.12 and the reverse direction characteristic of the mixer diode D.sub.11. The similar function works when the mixer circuit block M1 receives a band. Accordingly, it is possible to check that each band mixer circuit block operates normally in receiving the band.

In the figure, L.sub.11 through L.sub.16, L.sub.21 through L.sub.26 and L.sub.31 are reactance, D.sub.11 and D.sub.21 are mixer diodes, R.sub.11 and R.sub.12 are resistors, C.sub.11, C.sub.13, C.sub.23 and C.sub.33 are capacitors, and D.sub.23 and D.sub.22 are diodes.

According to the present invention, as mentioned above, the multiple-band mixer circuit contains a monitor circuit for common use by each band mixer circuit block, making it possible to check each band mixer circuit block for normal operation. Since one monitor circuit is shared by multiple mixer circuit blocks, the circuit can be made small in size.

Thus, this invention provides a small, effective multiple-band mixer circuit which shares a parallel circuit of a resistor and a capacitor for monitoring diode current for each band, the parallel circuit monitoring each band accurately.

While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as claimed.