EP0066076A1
Expired / Lapsed
EP
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Integrated circuit FSK modem
Assignee: Texas Instruments Inc
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Filing: 1982-04-20
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Granted: —
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Expires: 2002-04-20
Abstract
Abstract An integrated circuit FSK transmitter and receiver combination form a modem for receiving and transmitting FSK signals. The FSK transmitter has a square wave generator (11, 12, 13) for providing a clock output at a "mark" frequency or at a "space" frequency within a first frequency band. This clock output is shaped through a bandpass filter, (15, 16) shared with the FSK receiver, to provide an FSK output signal which is output through a low pass filter (20). The input FSK signal is received through a low pass filter (19) and then filtered through the band pass filter (15, 16). One section of the band passfilter (15, 16) accommodates the clock output while another section accommodates the FSK 'input, including an automatic gain control circuit (17). The band pass filter is connected to an integrated circuit demodulator (18) to provide a filtered sine wave thereto at either a mark or a space frequency within a second frequency band. The demodulator determines whether the sine wave is at a mark or a space frequency.
Inventors
- 👤 Kerry A. Hanson
- 👤 William A. Severin
- 👤 Donald C. Richardson
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-27 23:00
CPC Classifications
H; H04; H04L; H04L27/00; H04L27/10
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
130 words
Claim 1. An integrated circuit FSK modem for receiving and transmitting FSK signals, characterized in that there is provided: (a) clock means for providing a clock output at a frequency within a first frequency band; (b) input means for receiving an input FSK signal at a frequency within a second frequency band; (c) band pass filter means, having a first section for receiving the clock output to filter and provide an output FSK signal, and having a second section for receiving the FSK input signal to filter and provide a sine wave output; (d) output means for transmitting the output FSK signal; and (e) demodulating means to receive the sine wave output for determining whether its frequency within the second frequency band corresponds to a mark or a space indication.
Claim 2
Dependent Claim
36 words
Claim 2. The modem of Claim 1 wherein the clock means is characterized by: (a) (i) oscillator means; and (ii) square wave generating means for generating a square wave clock signal at the desired carrier frequency.
Claim 3
Dependent Claim
18 words
Claim 3. The modem of Claim 2 wherein the input means is characterized by a low pass filter.
Claim 4
Dependent Claim
71 words
Claim 4. The modem of Claim 3 wherein the band pass filter means is characterized by: (c) (i) input multiplexer means for selecting the first section for receiving the clock output and the second section for receiving the FSK input signal; and (ii) output multiplexer means for selecting the output FSK signal for transmission to the output means, and for selecting the sine wave output for transmission to the demodulating means.
Claim 5
Dependent Claim
18 words
Claim 5. The modem of Claim 4 wherein the output means is characterized by a low pass filter.
Claim 6
Dependent Claim
84 words
Claim 6. The modem of Claim 5 wherein the demodulating means is characterized by: (c) (i) mark filter means for receiving and filtering the sine wave output; (ii) space filter means for receiving and filtering the sine wave output; (iii) and a demodulating circuit for comparing the energy output signal of the mark filter means at a first frequency with the energy output signal of the space filter means at a second frequency for converting the output of the comparison means to digital data.
Claim 7
Dependent Claim
44 words
Claim 7. The modem of Claim 6 futher characterized in that there is provided: (d) automatic gain control means connected to receive the sine wave output for adjusting the sine wave (e) carrier detect means for detecting the presence of the FSK input signal.
Claim 8
Dependent Claim
70 words
Claim 8. The modem of Claim 7 wherein the demodulating circuit is characterized by: a positive full wave rectifier for receiving th'e first frequency signal and for providing a positive full wave rectification thereof; a negative full wave rectifier for receiving the second frequency signal and for providing a negative full wave rectification thereof; and means for summing the positive and negative full wave rectifications to provide the binary output.
Claim 9
Dependent Claim
326 words
Claim 9. The modem of Claim 8 wherein the means for summing is characterized by an operational amplifier, wherein the positive full wave rectifier is further characterized by: reference crossing detect means for detecting when .the first frequency signal crosses a predetermined reference in a positive direction, and for providing a first output signal in response thereto; first output signal storing means,-for storing the first output signal; first frequency signal storing means for storing the first signal; and inverting and non-inverting transfer circuitry, connected to the first output signal storing means, to the first frequency signal storing means and to the means for summing, for inverting and transferring the contents of the first frequency signal storing means to the summing means in the presence of the first output signal stored in the first output signal storing means, and for transferring, without inverting, the contents of the first frequency signal storing means to the summing means in the absence of the first output signal stored in the first output signal storing means; and wherein the negative full wave rectifier is characterized by: . reference crossing detect means for detecting when the second frequency signal crosses a predetermined reference in a negative direction, and for providing a second output signal in response thereto; second output signal storing means for storing the second output signal; second frequency storing means for storing the second frequency signal; and inverting and non-inverting transfer circuitry, connected to the second output signal storing means, to the second frequency signal storing means and to the means for summing, for inverting and transferring the contents of the second frequency signal storing means to the summing means in the presence of the second output signal stored in the second output signal storing means, and for transferring, without inverting, the contents of the second frequency signal storing means to the summing means in the absence of the second output signal stored in the second output signal storing means.
Claim 10
Dependent Claim
133 words
Claim 10. The modem of Claim 7 wherein the automatic gain control means is further characterized by: (d) (i) switchable gain impedance means for receiving the input signal; (ii) filter means incorporating the switchable gain impedance means, for providing a filtered output signal; (iii) output signal comparison means for receiving and comparing the output signal with the predetermined omplitude and for providing an UP signal if the output signal is too small, and a DOWN signal if the output signal is too large; and (iv) switchable gain adjusting means, connected to the switchable gain impedance means, for increasing or decreasing the impedance to increase the gai-n of the filter means if the output signal is too small, and to decrease the gain of the filter means if the output signal is too large.
Claim 11
Dependent Claim
46 words
Claim 11. The circuit of Claim 10 wherein the switchable gain impedance means is characterized by a capacitor ladder network wherein capacitors may he-switched in and out of the circuit to vary the impedance and to increase or decrease the gain of the filter means thereby.
Claim 12
Dependent Claim
19 words
Claim 12. The modem of any of Claims 1-12 wherein the band pass filter means comprises switched capacitor filters.
References Cited (Backward Citations)
FR2390786A1
Cited
US4142245A
Cited
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