Premodulation filter for generating a generalized tamed frequency modulated signal

• US 4,531,221 A
• Filed: 03/24/1983
• Issued: 07/23/1985
• Est. Priority Date: 04/13/1982
• Status: Expired due to Term

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Chung, Kah-Seng, Zegers, Leo E.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US06/478,397
• Time in Patent Office: 852 Days
• Field of Search: 375/11, 375/18, 375/17, 375/53, 375/60, 375/86, 329/104, 364/724, 333/18
• US Class Current: 375/296
• CPC Class Codes: H04L 25/497 by correlative coding, e.g. partial response coding or echo modulation coding transmitters and receivers for partial response systems transversal equalizers at the transmitter end H04L25/03343
• CPC Class Codes: H04L 27/2017 in which the phase changes are non-linear, e.g. generalized and Gaussian minimum shift keying, tamed frequency modulation H04L27/201 takes precedence

Abstract

A transmitter for transmitting a carrier whose frequency is modulated by pseudo five-level signals. In order to obtain a simple receiver and an improved signal-to-noise ratio, a substantially three-level signal is generated in the transmitter at the detection instants t=(2m-1)T/2 by means of a pre-modulation filter.

Claims

1. In a system of frequency modulating a carrier signal with a data signal, which data signal has five signal levels when sampled at sampling instants t=nT, where T is the bit period of said data signal, and n is the number of bits of said data signal, a premodulation filter, to which are incoming data signal to be transmitted is applied, for supplying said data signal, said data signal now having three signal levels when sampled at sampling instants (2m-1)T/2, where m is an integer, comprising:

a non-recursive second order digital filter connected to receive said incoming data signal and providing first and second delayed signals, means for multiplying said first signal by a factor A, and said second signal by a factor B, where B lies between a value of 0.54 and 0.66, and wherein 2A+B=1, means for multiplying said incoming data signal by a factor A forming a third signal, and means for combining said third signal with said multiplied first and second signals to provide an oupput signal; and

a lowpass filter which satisfies the third Nyquist criterion realized by means of a raised cosine filter satisfying the first Nyquist criterion having a roll-off coefficient, rb, between 0.2 and 0.42, said lowpass filter receiving said output signal from said digital filter and supplying said data signal.

2. The premodulation filter of claim 1 wherein said first and second delayed signals are provided from a series circuit of first and second delay elements each having a delay of T seconds.