JPH10335934A - Local oscillator circuit of satellite broadcast receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a circuit which expands the band width of an oscillation frequency, without using a part that changes an oscillation frequency by curving the parts of a micro-strip line that becomes a central conductor to be curved with a prescribed radius of curvature to extend the oscillation frequency. SOLUTION: A strip conductor circuit 52 has the form of a U-shaped, and curved parts are performed processing to curve with a prescribed radius of curvature R. Thereby, a micro-strip line that has the circuit 52 has a small characteristic impedance because the curved parts are performed R processing. Also, the larger the radius of curvature is, the smaller a standing wave ratio becomes, and a characteristic impedance also becomes small. That enables increasing oscillation frequency band width, without changing a used part or increasing cost. In the case of a strip circuit whose curved parts have right angles, electric field density converges on the curved parts, and the characteristic impedance of the parts becomes large.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a local oscillation circuit and an RF circuit used for a DBS tuner of a satellite broadcast receiver.
More particularly, the present invention relates to a local oscillator circuit using a microstrip line formed on a printed circuit board as a center conductor or a distributor.

[0002]

2. Description of the Related Art In a general satellite broadcast receiving system, a 12 GHz band radio wave transmitted from a satellite is first collected by a BS antenna, and the frequency is converted into a 1 GHz band (900 to 2150 MHz) high frequency signal by a BS converter. Next, the DBS tuner selects a desired signal band from the 1 GHz band signal from the BS converter and converts the selected signal into an intermediate frequency signal (479.5 MHz). Here, DBS stands for Direct Broadcasting Satellite,
A system that receives broadcasts from artificial satellites directly.

The bandwidth of the oscillation frequency required for a local oscillation circuit of a DBS tuner used for a satellite broadcast receiver is one of the conventional ones.
100 MHz (1429.5 MHz to 2529.5 MH)
z), but with the recent increase in the number of channels, DB
Since the input frequency of the S tuner has been expanded, the oscillation frequency band of the local oscillation circuit has been increased to 1250 MHz (1379.5 MHz).
Hz to 2629.5 MHz).
Therefore, conventionally, it was necessary to use a varicap diode having a large capacitance change ratio or a transistor having a high f _T (transition frequency).

FIG. 7 is a block diagram showing an example of a conventional local oscillation circuit. In FIG. 7, in a local oscillation circuit that oscillates a relatively high frequency, it is possible to use a microstrip line patterned on a printed circuit board as the center conductor L. However, since the analysis in FIG. 7 is complicated in a λ / 2 oscillation circuit, a λ / 4 oscillation circuit as shown in FIG. 8 is considered for simplicity.

Here, the resonance frequency is 1 / (ω (C _B + C _O )) = Z _O · tan (2π · 1 / λ) (1) ω: angular frequency (ω = 2πf, f: resonance frequency) C : Total capacitance Zo: Characteristic impedance l: Length of center conductor λ: Wavelength Here, the varicap diode which varies in the capacitance value by the reverse bias voltage, by using the C _B, so that to vary the oscillation frequency.

[0006]

However, the CV characteristic of this varicap diode shows a characteristic that the change in capacitance is small in a region where the reverse bias voltage is large, and the oscillation frequency hardly changes. Therefore, in order to expand the bandwidth of the oscillation frequency, it is sufficient to use a varicap diode having a large capacitance change ratio,
Generally, a varicap diode having a large capacitance change ratio has a large rs (equivalent series resistance) and is likely to stop oscillation. There is also a method of extending the oscillation frequency by using a transistor having a high f _T , but this increases the cost and the cost of the product.

It is an object of the present invention to provide a local oscillation circuit of a satellite broadcast receiver which can expand the oscillation frequency bandwidth without using a component for changing the oscillation frequency.

[0008]

According to the present invention, there is provided a local oscillation circuit for a satellite broadcast receiver having a microstrip line formed on a printed circuit board as a center conductor. The bending portion of the microstrip line serving as the center conductor is curved with a predetermined radius of curvature.

The invention according to a second aspect is characterized in that the extension of the oscillation frequency is adjusted by changing the length of the radius of curvature.

[0010]

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

FIG. 1 is a block diagram of a DBS tuner provided with a local oscillation circuit according to the present invention. In FIG.
The input signal in the 1 GHz band applied to the input terminal 31 is supplied to an RF circuit unit 32, which is a broadband amplifier, an attenuator 33,
The light passes through a tracking filter 34 and is applied to a mixer 35. The local oscillation signal from the local oscillation circuit section 36 is input to a PLL (phase locked loop) 38 via a high-pass filter 37, and the PLL 38 outputs the local oscillation signal (1300 MHz to 255) of the local oscillation circuit section 36.
0 MHz) to perform phase lock.
The phase-locked local oscillation signal is input to a mixer (mixer) 35 and converted into an intermediate frequency signal (IF signal). This IF signal is applied to the IF circuit unit 40 and input to the demodulation unit 41. The demodulated signal is input to an output terminal 48 via a signal output line 47. Reference numeral 42 denotes a power input terminal, which is connected to the RF circuit unit 32, the mixer 35, the PLL 38, the local oscillation circuit unit 36, the IF circuit unit 40, and the demodulation unit 41. IF at this time
The frequency of the signal output is 479.5 MHz.

Here, the oscillation frequency band of the local oscillation signal is 1
250 MHz (1379.5 MHz to 2629.5 MH
z).

In the local oscillation circuit section 36, a patterned microstrip line is formed on a printed circuit board as a center conductor L as described in the related art. The oscillation frequency of the local oscillation circuit is determined by the characteristic impedance Z
_It changes by changing _O. Here, consider a microstrip line as shown in the sectional view of FIG. In this microstrip line, a strip conductor circuit 52 having a thickness t and a width W is formed on the surface of a flat substrate 51 having a thickness h of a dielectric material having a low dielectric loss using a printed wiring technique, and a flat surface is formed on the back surface. The conductor 53 is formed.

The characteristic impedance Z _O of the microstrip line on the printed circuit board is as follows: Z _O = 42.4 / (ε + 1) ^1/2 · ln (1+ (4h / W ₁ ) · (b + (b ² + aπ ² )) ^1/2 )) (2) where W ₁ = W + a · ΔW ΔW = t / π · (1 + ln (4 / ((t / h) ² + 1 /
(Π (W / t + 1.1)) ² ) ^1/2 )) a = (1 + 1 / ε) / 2 b = (14 + 8 / ε) /11.4 h / W ₁ ε: relative permittivity of the substrate. The present invention extends the oscillation frequency bandwidth by reducing Zo.

FIG. 3 is a schematic diagram showing an embodiment of a strip conductor circuit of a microstrip line in a local oscillation circuit according to the present invention. This strip conductor circuit 5
2 has a U-shaped shape, and an R process for bending a bent portion with a predetermined radius of curvature R is performed. Here, as a comparison target, consider a strip conductor circuit 55 in which a bent portion is processed at a right angle as shown in FIG. In the strip conductor circuit 55, the electric field density is concentrated because the bent portion is at a right angle, and the characteristic impedance at that portion increases. Compared with this, the microstrip line having the strip conductor circuit 52 of FIG. 3 has a reduced characteristic impedance because the bent portion is subjected to the R processing.
And, as the radius of curvature is larger, the SWR (Standing Wave R
atio) is reduced, and the characteristic impedance is also reduced.

FIG. 5 shows the relationship between the resonance frequency and the resonance capacitance (C = C _B + C _O ) when Zo is used as a parameter. For example, if the resonance capacitance changes from Ca (pF) to Cb (pF) by an externally applied voltage, the resonance frequency becomes Zo =
When 100 (Omega), changes from f ₁ to f _2, Zo = 50
At (Ω), it changes from f ₃ to f ₄ . Here, each resonance frequency width is {f ₂₁ = f ₂ −f ₁ = 1150 MHz,
f ₄₃ = f ₄ −f ₃ = 1400 MHz. That is, the resonance frequency bandwidth can be increased by reducing the characteristic impedance.

As described above, by performing the R process for bending the bent portion of the center conductor L with a predetermined radius of curvature, it is possible to increase the oscillation frequency bandwidth without changing the parts used and increasing the cost of the tuner. Becomes Also,
By changing the radius of curvature, the oscillation frequency bandwidth can be adjusted.

FIG. 7 is a graph showing tuning voltage vs. oscillation frequency characteristics when the center conductor L has a pattern shape as shown in FIGS. 3 and 4 (R = 1.2 mm, W = 1.5) in the oscillation circuit of FIG. 6 is shown. It was confirmed that the oscillation processing increased the oscillation frequency bandwidth by about 100 MHz by performing the R processing.

[0019]

As described above, according to the first aspect of the present invention, since the bending portion of the microstrip line is bent with a predetermined radius of curvature, the characteristic impedance is reduced, and the used component can be changed or the tuner can be changed. It is possible to increase the oscillation frequency bandwidth without increasing the cost.

According to the second aspect of the present invention, since the extension of the oscillation frequency is adjusted by changing the length of the radius of curvature, a desired oscillation frequency can be obtained without providing an adjusting component. Cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of a DBS tuner including a local oscillation circuit according to the present invention.

FIG. 2 is a sectional view of a microstrip line of a local oscillation circuit.

FIG. 3 is a schematic diagram showing one embodiment of a strip conductor circuit of a microstrip line in a local oscillation circuit according to the present invention.

FIG. 4 is a schematic view of a main part of a strip conductor circuit in which a bent portion is processed at a right angle.

FIG. 5 is a graph showing a relationship between a resonance frequency and a resonance capacitance when impedance is used as a parameter.

FIG. 6 is a graph showing characteristics of tuning voltage versus oscillation frequency when the center conductor has a pattern shape as shown in FIGS. 3 and 4;

FIG. 7 is a block diagram illustrating an example of a conventional λ / 2-type local oscillation circuit.

FIG. 8 is a block diagram showing an example of a conventional λ / 4 type local oscillation circuit.

[Explanation of symbols]

 51 flat board 52 strip conductor circuit 53 flat conductor

Claims (2)

[Claims] In a local oscillation circuit of a satellite broadcast receiver having a microstrip line formed on a printed circuit board as a center conductor, a bending portion of the microstrip line is bent with a predetermined radius of curvature in order to extend an oscillation frequency. A local oscillation circuit for a satellite broadcast receiver. 2. An elongation of an oscillation frequency is adjusted by changing a length of the radius of curvature.
A local oscillation circuit of the satellite broadcast receiver described in the above.