Temperature stabilized oscillator and proximity switch containing the oscillator

A proximity switch, comprising:

• a temperature stabilized oscillator circuit, including a resonant circuit having a coil with a temperature dependent copper resistance (R.sub.CU) and an amplifier circuit connected as a virtual negative resistance, said oscillator circuit comprising;
• a current source connected in series with the resonant circuit in order to provide across the coil of the resonant circuit a voltage (U.sub.CU) which is directly proportional to the resistance of the coil of the resonant circuit;
• and
• a control circuit which in response to said voltage makes the virtual negative resistance substantially inversely proportional to the resistance of the coil of the resonant circuit, characterized in that the control circuit adjusts an output voltage (U.sub.e1) of the amplifier circuit based upon a voltage (U.sub.e2) that is a linear function of said voltage (U.sub.CU).

A temperature stabilized oscillator, including a resonant circuit (L, C, R.sub.CU) having a coil with a temperature dependent copper resistance (R.sub.CU) and an amplifier circuit (V, R.sub.1, R.sub.2, R.sub.3) connected as a virtual negative resistance (R.sub.n), said oscillator comprising:

• a current source (I.sub.1) connected in series with the resonant circuit (L, C, R.sub.CU) in order to provide a signal (U.sub.CU) which is a measure for the resistance (R.sub.CU) of the coil (L) of the resonant circuit;
• and
• a control circuit (V.sub.1, M;
• V.sub.2, V.sub.3, M) which by using said signal makes the virtual negative resistance (R.sub.n) substantially inversely proportional to the resistance (R.sub.CU) of the coil (L) of the resonant circuit, characterized in that the control circuit (V.sub.1, M;
• V.sub.2, V.sub.3, M) multiplies the output voltage (U.sub.e1) of the amplifier circuit (V, R.sub.1, R.sub.2, R.sub.3) with a voltage that is a linear function of said signal (U.sub.CU).

A temperature stabilized oscillator, including a resonant circuit (L, C, R.sub.CU) having a coil with a temperature dependent copper resistance (R.sub.CU) and an amplifier circuit (V, R.sub.1, R.sub.2, R.sub.3) connected as a virtual negative resistance (R.sub.n), said oscillator comprising:

• a current source (I.sub.1) connected in series with the resonant circuit (L, C, R.sub.CU) in order to provide a signal (U.sub.CU) which is a measure for the resistance (R.sub.CU) of the coil (L) of the resonant circuit;
• and
• a control circuit (V.sub.1, M;
• V.sub.2, V.sub.3, M) which by using said signal makes the virtual negative resistance (R.sub.n) substantially inversely proportional to the resistance (R.sub.CU) of the coil (L) of the resonant circuit, characterized in that the resonant circuit (L, C, R.sub.CU) is connected to one input of a first amplifier (V), a first resistor (R.sub.1) is connected to the other input of said first amplifier (V), a second resistor (R.sub.2) is connected between said other input of the first amplifier (V) and its output, a third resistor (R.sub.3) is inserted between said one input of said first amplifier (V) and the control circuit (V.sub.1, M;
• V.sub.2, V.sub.3, M), and that said one input of the first amplifier (V) and its output are connected to the control circuit (V.sub.1, M;
• V.sub.2, V.sub.3, M).