JPH0376605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an electrically heatable window heating element, which is not specifically configured as an antenna, in particular to a rear window heating unit (defroster) for a motor vehicle, which provides a broadband effective RF reception. to be able to be used as an antenna, but also to heat (demist) the one-sided window unit (if desired);
Relating to the field of electrical signal separation devices, or separation and matching devices.

PRIOR ART According to U.S. Pat. No. 4,086,594, an apparatus in the field of the invention is known and an electrical signal isolating apparatus is provided for isolating an RF signal from a heating current of an electrically heated window, and here includes the use of an isolation or blocking circuit that includes two interconnected coils that provide a high impedance path for common mode fluctuating currents, but not for automotive DC currents. The interconnected coil arrangement provides a low resistance path for current flowing from the
On the other hand, passing current from a DC power supply to the heating element, such a drawing device is used to enable the heated rear window of a car to be used as a radio antenna and for heating.

Another device in the field of the invention is disclosed in U.S. Pat.
No. 4,422,077, in which an improvement to the device according to said US patent is disclosed.

Such improvements are concerned with enabling electrically heatable automobile windows to be used as transmitting antennas at AM or VHF/FM wavelengths and effectively matching the impedance of the window heating element to the antenna feed circuit of the transmitter. Contains a matching tuning circuit to effectively transmit VHF signals received from the electrically heated window of the vehicle to the antenna input terminal. The improvements presented herein also operate in combination with isolation circuits having interconnected coils.

OBJECTS OF THE INVENTION The present invention provides further advantageous and improved arrangements in this field of invention and makes further specific improvements to the apparatus disclosed in the aforementioned US patents.

SUMMARY OF THE INVENTION According to the present invention, a novel separation and matching device comprises:
To enable a heating element of an electrically heatable window of a motor vehicle, which is not specifically configured as an antenna, to be used as a wide-bandwidth receiving antenna in the VHF band. This device has an input lead that connects to the vehicle's DC power source, an output lead that connects to the heating element, an antenna terminal that connects to the antenna feed circuit of the receiver, and an output that is coupled to the input and output leads and output from the input lead. It has a separation circuit that passes DC power to the lead wire but does not pass RF signals from the output lead wire to the input lead wire, and an antenna matching circuit inserted between the output lead wire and the antenna terminal, and has the following characteristics. has. That is, the matching circuit has components to be connected to the heating element so as to form a circuit which, in conjunction with the heating element, resonates near the center of the band within the VHF range, and which circuit is a resonant circuit. The impedance of the antenna is matched to the input impedance of the antenna feed line.

In one aspect of the invention, which is a series VHF matching structure, the matching circuit causes the heating element to be series resonant near the center of the VHF band. In other words, electrically heated car windows are compatible with the above-mentioned parts.
Creates series resonance within the VHF band and is effective
It can be used as a VHF receiving antenna.
The matching circuit also has a parallel resonant circuit connected directly to the component to provide an even more nearly optimal matching.

According to a second aspect of the invention, which is a shunt VHF matching structure, the matching circuit includes a separate circuit impedance that causes the heating element to resonate near the center of the VHF band. In other words, an electrically heatable automobile window can interact with the above components to create parallel resonance within the VHF band and can be used as an effective VHF receiving antenna. The matching circuit also includes a parallel resonant circuit that operates in tandem with the components to provide VHF broadband matching characteristics.

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

First, according to FIG. 1, the series VHF according to the present invention
A matching structure is shown.

For convenience, the operation of the apparatus shown in FIGS. 1 and 2 will be described in four sections below.

SIGNAL FREQUENCY INPUT AND MATCHING CIRCUIT The electrically heated windows of the vehicle and the heating elements therefor (not shown) are connected at the relevant frequency to two bi-heater coil circuits from the vehicle's DC power supply means connectable to the top of the capacitor C3. Means L
1 and L2, these circuit means may then be a bi-eye latch yoke. Coil L1 has a ferrite rod core and is largely or approximately self-resonant in the VHF band, while coil L2 has a ferrite pot core and has a large impedance at frequencies in the AM band. Furthermore, capacitor C3
is provided for decoupling the heater feed line connected to the top of this capacitor. Capacitors C1 and C2 connect the two illustrated paths leading to the terminal leads of the window heating element in parallel with respect to the signal frequency. Parts L3 and C5 are
Together with the leakage inductance of coil L4 with taps, the electrically heatable window and/or heating element therefor is adapted to resonate in series near the center of the VHF band. This series resonance characteristic is
Together with the parallel resonant circuit L4-C7, it forms a nearly optimal matching circuit which couples the terminal leads of the heating element to the input terminals of the VHF amplifier means designated TR2. Component C5 connected between coil L3 and tapped coil L4 has a compromise value and is effectively connected to the VHF amplifier input terminal.
A small value is desirable to prevent the AM signal from reaching the AM amplifier input terminal, and in this regard reduce the capacitive loading on the AM amplifier input terminals, but if the value is too small,
The reactance gradient of the series resonance in VHF increases and the available bandwidth and performance are compromised. The impedance characteristics of coil L1 are
VHF signals are effectively blocked, but AM signals are allowed to pass freely and are supplied by capacitor C4 to AM amplifier means TR3.

The VHF amplifier junction FET TR2 operates with its gate grounded with respect to the signal frequency and is bypassed by a capacitor C8. The source of FET TR2 is directly connected to the input matching circuit, ie to the connection point of components L4-C7 as shown in FIG. The drain has an inductance L5,
The inductance L5 is connected to an RF output circuit line having an antenna terminal (not shown) for connection to the antenna feeding circuit of the radio receiver.
is the impedance of the cable that resonates near the center of the VHF band together with the drain capacitance including stray components, and that is connected to the radio receiver and supplies power (e.g.
100Ω) and the drain of FET TR2. Capacitor C9 blocks the amplifier supply voltage at the drain from reaching the RF signal output line, and the amplifier supply voltage is supplied to the circuit at the +12V point shown to the right of coil L8.

AM band amplifier The bipolar transistor TR3 operates as an emitter follower stage, and the base is connected via the resistor R1.
AM is connected to input coupling capacitor C4, while the output terminal is connected to blocking capacitor C10 and ferrite inductance or chiyoke L7.
Connects from Emitsuta to the radio receiver via
Connected to the RF output line connection. Inductance L7 is self-resonant in the VHF band and effectively prevents the low output impedance of AM amplifier TR3 from loading the output of VHF amplifier TR2. The reactance of the VHF output capacitor C9 is large enough to prevent AM signals from penetrating the drain current of the VHF amplifier in the AM band. The resistor R1 is used to prevent high frequency parasitic vibrations in the AM amplifier, and for convenience of the printed circuit board structure of this circuit, the resistor R1 is
It may also be replaced by two independent resistors connected in series with each other, each having a value of 47Ω.

Bias Supply Circuit To reduce the effects of variations in the operating parameters of the illustrated unit, the portion of this circuit centered around Zener diode D1 and transistor TR1 operates in conjunction with associated resistors R5 and R3 to produce a stable bias supply voltage. However, this bias supply voltage is supplied to the gate of FET TR2 and to the base of transistor TR3 via resistor R4, and a current source is connected to the source of FET TR2. The operating parameters of the amplifier circuit vary negligibly, but within the normal range of power supply voltage variations normally occurring in automobiles. Noises and disturbances possibly caused by the supply voltage supplied to said points from an automotive DC power supply or other suitable power source are filtered by filter component L8,
That is, it is eliminated by the ferrite inductance and capacitor C11. The Zener diode D3 provides protection against possible high voltage transients and reverse polarity connections at the supply voltage. Furthermore, the smoothed supply voltage formed thereby for filter components L8 and C11 is supplied directly to the collector of the AM amplifier TR3 and is connected to the VHF
It is supplied to the drain of FET TR2 via a ferrite inductance or a choke L6. In the circuit configuration of FIG. 2, two further protective devices are provided, namely a neon tube element and a diode D2, which in any individual or simultaneous operation prevent the electric heating of the motor vehicle from being The window heating elements are connected as shown for protection in case of electrostatic discharge.

In conjunction with said separation circuit means of this embodiment, there are provided interconnected coils, these coils being bifilar windings, toroidal or U-shaped cores wound with two identical interconnected windings. can have. The matching and decoupling circuit is hereby obvious to the person skilled in the art; for example, instead of the interconnected coil circuit means, a bifilar component L2 in the form of a closed magnetic circuit may be substituted.

According to the exemplary embodiments illustrated in FIGS. 1 and 2, therefore, the heating element of the heatable window of a motor vehicle, which is not specifically constructed as an antenna and is essentially non-tunable and non-resonant at RF frequencies, comprises:
It can now be used as an effective VHF receiving antenna, and can also receive AM signals with a suitable receiver.

Although the coils L1 and L2 have been described as bifilar coil devices with ferrite cores, one has a ferrite rod core and the other has a ferrite pot core, as previously stated. be.

3 and 4, a shunt VHF matching structure is shown. Compared to the series matching structure described in FIGS. 1 and 2, the most important aspects of the shunt matching structure are the modification of the VHF matching circuit and the connection relationship with the isolation circuit. Depending on the dimensions and detailed structure of the electrically heatable motor vehicle window unit and depending on the frequency range of the VHF band in question, the electrically heatable motor vehicle window unit can be used as an antenna and integrated into the overall matching circuit. In some cases, it may be further advantageous to operate as a parallel resonant circuit. In this regard, the bi-eyeline inductance L1 is placed in parallel with the window heater via the terminal lead wire and resonates near the center of the VHF band.

The operation of the device shown in FIGS. 3 and 4 for convenience is as follows:
Next, the explanation will be divided into four sections.

Signal Frequency Input and Matching Circuits Depending on the dimensions and details of the electrically heatable vehicle window unit and the pattern of the heating elements, i.e. the dimensions, type and location of the window unit and heating elements in the particular vehicle, the above It is therefore advantageous to operate the window unit as a parallel resonant circuit. Therefore, the inductance of the bifilar coil means L1, together with the reactance of the 68 pF capacitor Ca, are arranged and connected in such a way that they resonate with each other and with the window heater unit near the center of the VHF band. The value of capacitor Ca is a design compromise. This is because too small a value will increase the susceptance gradient and result in loss of bandwidth/characteristics within the VHF band, and a large value of this capacitor will make the AM characteristics dangerous. For convenience of explanation, L1
The above operation of Ca and Ca can be described as having a parallel resonance near the center of the VHF band, and this resonance is formed at the heater terminal lead connection. This parallel resonance is coupled to the second parallel resonant circuit means L4-C5 by capacitor C5, resulting in a broadband matching characteristic. The actual values of the above parts L1, L4, C5 and C7 and Ca depend on the car model and/or
or may vary depending on the type and dimensions of the electrically heatable window unit.

VHF amplifier Junction FET T2 operates in a gate-grounded circuit with respect to the signal frequency, bypassing being provided by capacitor C8. The source of FET T2 is directly connected to said component of the matching circuit;
In particular, it is connected to tapped coil L4.
The drain of FET T2 is connected to the RF output circuit line including the antenna terminal (not shown) by a ferrite inductance L5, and this ferrite inductance, together with the drain capacitance including stray components, is connected near the center of the VHF band. Provides a near-optimal match between the impedance of the cable that is resonant and feeding the radio receiver or the impedance of the antenna feed circuit (eg, approximately 100Ω) and the drain of FET T2. Capacitor C9 is
The amplifier supply voltage on the drain side of FET T2 is blocked so that it does not reach the lines of the RF signal output circuit, and such amplifier supply voltage is added to the 12V connection point on the right side of coil L8 as shown in Figure 4. It will be done.

The AM band amplifier FET T3 operates as a source follower stage, and the gate is connected to the input coupling capacitor C4 via the resistor R1.
On the other hand, the output side, that is, the drain side, is connected to the line from the source to the RF output connector via the blocking capacitor C10 and the ferrite inductance L7. Inductance L7
is self-resonant within the VHF band and substantially
The low output impedance of AM amplifier means T3
Avoid loading the output of the VHF amplifier means T2. The reactance of VHF output capacitor C9 is large enough in the low frequency AM range to prevent AM signals from entering the drain supply of VHF amplifier T2. Resistor R1 is FET
This is used to prevent high frequency parasitic vibration from occurring in the T3 AM amplifier circuit.

Bias Supply Circuit In order to reduce the influence of the operating parameters of said configuration on supply voltage fluctuations and variations in FET parameters, the circuit section centered around Zener diode D1 and bipolar transistor T1, with associated resistors R3 and R5, is connected to FET T2 and The current source operates to provide a stable bias voltage supply for the gate of T3, as shown in FIG.
Connected to the source of FET T2. The operating parameters of the amplifier circuit vary negligibly, but within the normal range of supply voltage fluctuations that normally occur in motor vehicles. Noise and disturbances in the automotive DC power supply or similar amplifier supply voltage means are filtered out by filter components L8 and C11. Zener diode D3 is
Protection is provided against possible high voltage transients and against reverse polarity connections of the amplifier supply voltage.
The amplifier feed voltage passed through the filter is supplied to the AM amplifier FET T3 as shown, and
It is supplied to the drain of the VHF amplifier T2 via a VHF ferrite inductance or a choke L6. Other protective devices are also in place.
This is the diode D2 which protects the electrically heated window unit and its heating element in the event of electrostatic discharges during operation.

Variations and improvements in the shunt matching structure will be obvious to those skilled in the art, and in this regard the isolation circuit consists of a toroidal or U-shaped core wound with two identical coils interconnected with a bifilar winding. With mutually coupled coils, either type of device can substitute for coil L2 in a closed magnetic circuit.

The series and shunt VHF matching structures as mentioned above are
both having matching circuit means operative to effectively match the impedance of the electrically heatable vehicle window heating element to the antenna input impedance of the antenna feed circuit of the radio receiver; This enables effective VHF signal reception. Further in this connection, the VHF band amplifier means of each of these structures also include:
A mode of operation as described above is used to achieve this purpose. The VHF amplification transistors are selected to have a low noise figure, and the matching circuit is configured to yield as much of the source impedance as possible to the optimal low noise source impedance for the device.

To help you better understand the similarities and differences between shunt-matched and series-matched structures, functionally equivalent parts are shown with similar part numbers in Figures 4 and 2, respectively. Be careful that there are.

Furthermore, with regard to FIG. 4, the following is taken into consideration in order to designate and describe the values of parts when designing the above embodiment.

L1 4+4 turns, diameter 9.5mm, wire 1.6mm L2 10-1/2+10-1/2 turns, 30mm ferrite pot core, wire 1.4mm, 1.2~1.4mH L4 4+4 turns, diameter 6mm, wire 0.5mm L5 8 turns, resonant at 98MHz in circuit L6 16 turns, self-resonant at 98MHz in circuit L8 1mH Chiyo Inductance The above values are an example for a particular model.

The embodiments described above regarding series matching and shunt matching, and in particular the construction of their respective matching circuits, do not apply in principle, unless the overall required bandwidth is excessive.
Can be used to couple a window heater antenna to a VHF transceiver unit. Note, however, that satisfactory operation of a VHF transmitter requires a better matching quality than is normally acceptable for a receiver. Therefore, in relation to the natural resonance of the heater antenna (and the connecting leads to the matching circuit) in the frequency band in question, and the separation of the VHF transmit and receive frequencies, it is satisfactory when using a matching device or circuit with a single passband. It has been found that achieving sufficient characteristics as desired can be difficult. The series matching structure described above can be used with natural series resonant window elements, and the shunt matching structure can be used with natural shunt resonant window elements over the VHF band. In both cases the structure is designed for wideband VHF reception at approximately 88-108MHz.
and is designed for the 0.15-1.6MHz AM broadcast band.

Of course, it is clear that the invention is not limited to the details of the embodiments described above, which are only described by way of example.

For example, AM characteristics can be improved by providing a voltage tracking stage as shown in FIG.

The input impedance of this stage is high, in this case
It is largely dominated by the 10kΩ input bias resistor (R4 in Figure 2). in Bay Aira Coil
The AM output can thereby be stepped up without being severely loaded by the emitter follower input.

As shown in Figure 5, an extra coil is wound over the bifilar winding to form an autotransformer that steps up the AM voltage supplied to the base of the emitter follower. This extra coil consists of thin wire (approximately 0.15mm). Although the number of turns may be varied depending on specific conditions, a step-up ratio of 1:1.5 to 1:2.5 is appropriate. According to the extra coil of 9.5 turns, 1:
A ratio of 2 is obtained, giving a theoretical signal improvement of approximately 6 dB.

Further, FIG. 2 shows an emitter follower AM amplifier with a series matching structure, and FIG. 4 shows an AM source follower with a shunt matching structure.
It is clear that the opposite configuration may also be used (ie an AM source follower with a series VHF matching structure).

Furthermore, the names AM and FM used here should be understood as convenient names.
They represent a range of frequencies, namely lower medium wave frequencies and higher VHF frequencies, respectively. There is no necessity to limit the modulation method.

According to the above embodiments, it is clear that in all cases an effective VHF antenna can be obtained using a conventional heated window. No physical changes to the windows are required. Adaptation for VHF is done electronically using an isolation and matching circuit connected to the leads of the visible heating element and mountable at any suitable location near the window.

[Brief explanation of drawings]

1 is a simplified block diagram of a series VHF matching structure; FIG. 2 is a detailed circuit diagram of the device of FIG. 1;
3 is a simplified block diagram of a shunt VHF matching structure, FIG. 4 is a detailed circuit diagram of the apparatus of FIG. 3, and FIG. 5 is a diagram showing a modified configuration of the separate circuit inductance. C...Capacitor, L...Inductance coil, R...Resistor, T, TR...Transistor.

Claims (1)

[Claims] 1. An input lead wire connected to a DC power source of an automobile;
An output lead that connects to the heating element, an antenna terminal that connects to the antenna feed circuit of the receiver, an antenna terminal that connects to the input and output leads and passes DC power from the input lead to the output lead, but from the output lead to the input lead. an electrically heatable automobile window that is not specifically configured as an antenna and has a separation circuit (inductances L1, L2) that does not pass RF signals to the heating element of
In an isolating and matching device for use as a wide-bandwidth receiving antenna of at least 20 MHz in the VHF range, operating in series resonant mode, in which case a first inductance L3 and a first capacitor C5 connected in series are provided. The inductance and capacitor cause the window heating element to resonate in the center of the desired VHF band, and the first capacitor C5
is connected to the tap point of a parallel resonant circuit in the VHF band that includes a second inductance L4 and a second capacitor C7, and the entire circuit is
A third capacitor C6 provides a decoupling path for the amplifier bias supply and the amplifier TR2 is connected to the VHF amplifier TR2.
configured to produce a source impedance that is effectively matched to the characteristic impedance of the antenna feed line leading to the receiver;
Separation and alignment equipment. 2. The device of claim 1, wherein the separation circuit L1, L2 comprises at least one bifilar-wound coil. 3. Device according to claim 1, in which the separating circuit L1, L2 has a toroidal or U-shaped core wound with two interconnected coils. 4. Device according to one of the claims 1 to 3, characterized in that an AM band amplifier TR3 is provided to enable the receiver to receive AM signals. 5. The device according to claim 4, wherein bias supply circuits D1, TR1, R3, R5 are provided for the VHF band and AM band amplifiers. 6 Input lead wire that connects to the car's DC power supply,
An output lead that connects to the heating element, an antenna terminal that connects to the antenna feed circuit of the receiver, an antenna terminal that connects to the input and output leads and passes DC power from the input lead to the output lead, but from the output lead to the input lead. an electrically heatable automobile window that is not specifically configured as an antenna and has a separation circuit (inductances L1, L2) that does not pass RF signals to the heating element of
In an isolation and matching device that allows use as a wide-bandwidth receiving antenna of at least 20 MHz in the VHF range, a first inductance L operating in parallel resonant mode and connected to a first capacitor Ca
1, the capacitor and inductance provide RF signal isolation and cause the window heating element to resonate in the center of the desired VHF band, and the first inductance L1 is connected by a fourth capacitor C5. It is connected to a parallel resonant circuit in the desired VHF band that includes a second inductance L4 and a second capacitor C7, the whole circuit is connected from the tap point of the second inductance L4 to an amplifier T2, and the amplifier It is noted that the amplifier T2 is configured to provide a source impedance that is effectively matched to the characteristic impedance of the antenna feed leading to the receiver, with a third capacitor C6 providing a decoupling path for the bias supply. Features: Separation and alignment equipment.