Adaptive equalizer and/or antenna tuning
Equalization circuits and methods are implemented for a variety of applications. According to one such application, a transmitting device wirelessly communicates using an antenna. The device has a transmission circuit that is configured and arranged to transmit a first wireless signal using magnetic coupling between the antenna and a remote device, the coupling occurring over a wireless medium. A receiver circuit of the transmitting device is configured and arranged to receive a second wireless signal that is from the antenna and that represents the first wireless signal as modified by the coupling occurring over the wireless medium. An error circuit of the device is configured and arranged to generate an error signal by comparing the first wireless signal to the second wireless signal. An equalizer circuit of the device is configured and arranged to pre-code the first wireless signal with coding that compensates for inter-symbol interference by compensating for the error signal.
1. A device for wirelessly communicating using an antenna, the device comprising:
a transmission circuit configured and arranged to transmit a first wireless signal using magnetic coupling between the antenna and a remote device, the coupling occurring over a wireless medium;
a receiver circuit configured and arranged to receive a second wireless signal that is from the antenna and that represents the first wireless signal as modified by the coupling occurring over the wireless medium;
an error circuit configured and arranged to generate an error signal by comparing the first wireless signal to the second wireless signal; and
an equalizer circuit configured and arranged to pre-code the first wireless signal with coding that compensates for inter-symbol interference by compensating for the error signal.
2. The device of claim 1 , wherein the transmission circuit is further configured and arranged to format the first wireless signal according to a near-field communications protocol operating at data speeds of at least one Mbit/s.
3. The device of claim 1 , wherein the transmission circuit is further configured and arranged to generate two data signals x i and x q for use in a phase-shift keying (PSK) protocol.
4. The device of claim 1 , further including a finite-infinite response (FIR) filter configured and arranged to generate complex coefficients from the error signal, wherein the complex coefficients are generated to result in a frequency-independent transfer function resulting from the precoding and the coupling occurring over the wireless medium.
5. The device of claim 1 , further including a finite-infinite response (FIR) filter configured to include two zeros in transfer function of the FIR filter.
6. The device of claim 1 , further including a transfer function circuit that is configured and arranged to modify the first data signal according to a desired transfer function and wherein the error circuit is configured and arranged to compare the modified first data signal to the second wireless signal.
7. The device of claim 6 , further including a high-pass filter configured and arranged to suppress a carrier signal in the second wireless signal and wherein transfer function circuit is further configured and arranged to include a model of the high-pass filter in the desired transfer function.
8. The device of claim 1 , wherein the transmission circuit is further configured and arranged to format the first wireless signal according to a near-field communications protocol operating at data speeds of up to at least a data rate of 6.78 Mbit/s at a symbol rate of at least 1.695 Msym/s.
9. The device of claim 1 , further including a tuning circuit configured and arranged to adjust a resonant frequency of the antenna in response to the error signal.
10. The device of claim 9 , wherein the tuning circuit is configured and arranged to adjust the resonant frequency of the antenna by changing the value of a capacitive load connected to the antenna.
11. The device of claim 9 , wherein the tuning circuit includes one of a varicap diode and a switched bank of capacitors.
12. The device of claim 9 , wherein the tuning circuit is configured and arranged to integrate an imaginary component, w 2,q , of the error signal, and to use the result of the integration to control a tuning capacitor's value and thereby forcing the imaginary component w 2,q to converge to zero.
13. A bidirectional wireless communications device comprising:
a transmit path including
an equalizer circuit configured and arranged to pre-code a first digital data with coding that compensates for inter-symbol interference that is represented by an error signal;
a digital to analog converter circuit configured and arranged to produce an analog transmit signal from the pre-coded first digital data;
an up-conversion circuit configured and arranged to generate a passband signal by adding a carrier frequency component to the analog transmit signal; and
an amplifier circuit configured and arranged to provide an amplified version of the passband signal to an antenna; and
a receive path including
a down-conversion circuit configured and arranged to generate an analog receive signal by removing a carrier frequency component from the passband signal;
an analog to digital converter circuit configured and arranged to produce second digital data from the analog receive signal; and
an error circuit configured and arranged to generate the error signal by comparing the first digital data to the second digital data.
14. The device of claim 13 , wherein the digital to analog converter circuit includes the up-conversion circuit and the digital to analog converter circuit is further configured and arranged to add the carrier frequency component in a digital domain.
15. The device of claim 13 , wherein the analog to digital converter circuit includes the down-conversion circuit and the analog to digital converter circuit is further configured and arranged to remove the carrier frequency component in a digital domain.
16. The device of claim 13 , wherein the transmission path is further configured and arranged to format the first digital data signal according to a near-field communications protocol operating at data speeds of at least one Mbit/s.
17. The device of claim 13 , further including a tuning circuit configured and arranged to adjust a resonant frequency of the antenna in response to the error signal.
18. A method comprising:
transmitting, using a transmission circuit, a first wireless signal using magnetic coupling between the antenna and a remote device, the coupling occurring over a wireless medium;
receiving, using a receiver circuit, a second wireless signal that is from the antenna and that represents the first wireless signal as modified by the coupling occurring over the wireless medium;
generating, using an error circuit, an error signal by comparing the first wireless signal to the second wireless signal; and
pre-coding, using an equalizer circuit, the first wireless signal with coding that compensates for inter-symbol interference by compensating for the error signal.
19. The method of claim 18 , further including a step of adjusting, using a tuning circuit, a resonant frequency of the antenna in response to the error signal.