Low noise filter for a wireless receiver
First Claim
1. A low-noise filter for receiving a downconverted signal, comprising:
- a signal path extending from an input line to an output line;
a load capacitor in the signal path;
a frequency dependent negative resistance (FDNR) device coupled to the signal path;
a bias resistor coupled to the output of the load capacitor;
a bias voltage source coupled to the bias resistor; and
wherein the bias resistor and the bias voltage are used in setting a high cutoff frequency so that the load capacitor acts to block or cancel a DC offset in the downconverted signal.
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Accused Products
Abstract
A low noise filter is arranged to receive an input signal from a downconverter. The low noise filter is constructed to block or cancel any DC offset in the input signal, as well as filter selected frequency components from the input signal. The low noise filter uses a shared capacitor both to handle the DC offset and to set filter response characteristics. As the low noise filter is implemented with a Frequency Dependent Negative Resistance (FDNR) device, the shared capacitor may be relatively small. The low noise filter has a load capacitor, with the output of the load capacitor coupled to a bias resistor and voltage. This bias structure cooperates with the load capacitor to set a high cutoff frequency for the low noise filter useful for blocking or canceling the DC offset.
33 Citations
29 Claims
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1. A low-noise filter for receiving a downconverted signal, comprising:
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a signal path extending from an input line to an output line;
a load capacitor in the signal path;
a frequency dependent negative resistance (FDNR) device coupled to the signal path;
a bias resistor coupled to the output of the load capacitor;
a bias voltage source coupled to the bias resistor; and
wherein the bias resistor and the bias voltage are used in setting a high cutoff frequency so that the load capacitor acts to block or cancel a DC offset in the downconverted signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A low IF receiver portion having at least one low-noise filter, comprising:
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an input line for receiving an RF signal;
a down converter connected to the input line and having a low frequency output line, the down converter coupled to a local oscillator and arranged to generate a low frequency signal on the low frequency output line;
a low-noise filter coupled to the low frequency line, the low noise filter further including a capacitor arrangement and an FDNR device;
a bias resistor cooperating with the capacitor arrangement to form a DC blocking structure; and
an output signal line extending from the low noise filter to a demodulator module. - View Dependent Claims (9, 10)
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11. A method for filtering, comprising:
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providing a baseband signal having unwanted frequency components and a DC offset;
blocking the DC offset using a capacitor; and
filtering the unwanted frequency components using the capacitor. - View Dependent Claims (12, 13, 14, 15)
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16. An integrated circuit chip having active and passive components cooperating on a semiconductor substrate to perform a low noise filtering function, comprising:
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an input line for receiving a signal;
a capacitor block coupled to the input line and positioned on the integrated circuit chip;
an FDNR device cooperating with the capacitor block to add poles to a transfer function for the low noise filter; and
a bias structure cooperating with the capacitor block to block or cancel DC offset in the signal. - View Dependent Claims (17, 18)
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19. Baseband circuitry, comprising:
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an input line for receiving a filtered baseband signal;
control circuitry configured to operate on the filtered baseband signal, wherein the filtered baseband signal is generated according to the steps of;
providing an unfiltered baseband signal having unwanted frequency components and a DC offset;
filtering the unwanted frequency components using an FDNR device that cooperates with a capacitor to define poles in a filter transfer function; and
blocking the DC offset using a capacitor. - View Dependent Claims (20)
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21. A low noise filter module for filtering a downconverted signal, comprising:
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a signal path extending from an input line to an output line;
a load capacitor on the signal path;
a first filter stage coupled to the signal path and including a first FDNR device;
a second filter stage coupled to the signal path and including a second FDNR device;
bias circuitry coupled to the output of the load capacitor; and
wherein the bias circuitry cooperates with the load capacitor to block or cancel a DC offset in the downconverted signal. - View Dependent Claims (22, 23, 24, 25, 26, 27)
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28. A process for designing a low noise filter, comprising:
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selecting a passive filter topology and component values to meet a transfer function requirement, the passive filter having a load resistance, an inductor, and a capacitor;
converting the passive filter to an active filter using a Bruton transformation so that the load resistance is converted to a load capacitance, the inductor is converted to a resistance, and the capacitor is converted to an FDNR device; and
coupling a bias resistor to the output of the load capacitance; and
selecting a bias voltage for the bias resistor that sets a high pass cutoff to block a DC offset. - View Dependent Claims (29)
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Specification