Phase adjustable polyphase filters

A polyphase filter, comprising:

• a first phase splitting filter that produces a first output, the first phase splitting filter comprising a first RC network;
• a second phase splitting filter that produces a second output, the second phase splitting filter comprising a second RC network;
• a first variable resistance connected across the first output and a second variable resistance connected across the second output, the first variable resistance separate from the first RC network and the second variable resistance separate from the second RC network;
• and
• a detector that determines the phase of the first and second outputs, and adjusts the first variable resistance and the second variable resistance to produce a desired phase difference between the first output and the second output.

A communication system, comprising:

• a transmitter and a receiver, the transmitter comprising an input, an analog-to-digital converter, a digital signal processor, a digital-to-analog converter and an RF signal generator, the transmitter modulating an RF carrier with a signal provided to the transmitter input and transmitting the modulated RF carrier, the receiver comprising an RF input, a local oscillator, a polyphase filter connected to an output of the local oscillator, the polyphase filter producing first and second outputs from the local oscillator output, a mixer that combines the RF input with the first and second outputs of the polyphase filter, baseband circuitry, an analog-to-digital converter, and a digital signal processor that demodulates an output of the analog-to-digital converter, and produces a demodulated output,
• the polyphase filter including:
• a first phase splitting filter comprising a first RC network, the first phase splitting filter configured to provide a first output;
• a second phase splitting filter comprising a second RC network, the second phase splitting filter configured to provide a second output;
• a first variable resistance separate from the first RC network and the second RC network, the first variable resistance connected across the first output;
• and
• circuitry capable of detecting the phase of the outputs produced by the first and second outputs, and circuitry capable of adjusting the first variable resistance to produce a desired phase difference between the first output and the second output.

A polyphase filter, comprising:

• a first phase splitting filter comprising a first RC network, the first phase splitting filter configured to provide a first output, the first RC network including a first resistor in series connection with a first capacitor, the first resistor and the first capacitor directly connected together at a first node;
• a second phase splitting filter comprising a second RC network, the second phase splitting filter configured to provide a second output, the second RC network including a second resistor in series connection with a second capacitor, the second resistor and the second capacitor directly connected together at a second node;
• a first variable resistance separate from the first RC network and the second RC network, the first variable resistance connected across the first output, the first variable resistance connected to the first node;
• and
• circuitry capable of detecting the phase of the outputs produced by the first and second outputs, and circuitry capable of adjusting the first variable resistance to produce a desired phase difference between the first output and the second output.