Bandwidth controlled data amplifier

• US 4,608,542 A
• Filed: 06/06/1985
• Issued: 08/26/1986
• Est. Priority Date: 06/06/1985
• Status: Expired due to Fees

• Current Assignee: RCA Corporation
• Original Assignee: RCA Corporation
• Inventors: Siegel, Stefan A.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): Mottola, Steven J.
• Application Number:
  US06/741,874
• Time in Patent Office: 446 Days
• Field of Search: 250/214 A, 250/214 AG, 330/59, 330/279, 330/281, 330/282, 330/308, 455/619
• US Class Current: 330/279
• CPC Class Codes: H03G 3/3084 in receivers or transmitters for electromagnetic waves other than radiowaves, e.g. lightwaves H03G3/32, H03G3/34 take precedence

Abstract

A transimpedance amplifier for data signals from a high impedance source includes a forward voltage amplifier and a feedback resistance. The feedback includes an FET. The resistance of the FET is controlled by a control signal derived from the data signal at the output of the transimpedance amplifier by a differentiator which generates pulses for each data transition and an average detector which generates a control signal responsive to the number of transitions per unit time, which is the data rate. The resistance of the FET is high when the data rate is low, reducing the noise magnitude and decreasing the noise bandwidth. When the data rate increases, the resistance of the FET decreases, providing greater bandwidth for handling the signal. The change in gain caused by the bandwidth control tends to change the magnitude of the output data signal. This may be corrected by an AGC loop which controls the open loop gain of the voltage amplifier. In order to reduce the effect of differences in the bit transition time, a limiter may be coupled to the bandwidth control signal generator.

Claims

1. An amplifying arrangement for a data signal, comprising:

a voltage amplifier including signal input and signal output terminals and adapted for amplifying said data signal;

controllable feedback resistance means coupled between said signal input and signal output terminals of said amplifier to form a transimpedance amplifier;

differentiating means coupled to receive said data signal for generating a stream of differentiating pulses including a pulse in response to each transition of said data signal; and

control signal generating means coupled to said differentiating means and to said controllable feedback resistance means for generating a control signal for controlling said resistance means to reduce said resistance in response to increases in the number per unit time of said pulses and to increase said resistance in response to decreases in the number per unit time of said pulses whereby the resistance of said feedback means is responsive to the data rate of said data signal for selecting the bandwidth of said transimpedance amplifier.

2. An arrangement according to claim 1 wherein said control signal generating means comprises:

rectifying means coupled to said differentiating means for generating undirectional pulses in response to said differentiated pulse; and

averaging means coupled to said rectifying means for averaging said undirectional pulses for generating said control signal.

3. An arrangement according to claim 2 wherein said averaging means comprises capacitance means coupled for integrating a current representative of said undirectional pulses.

4. An amplifying arrangement for a data signal, comprising:

a voltage amplifier including signal input and signal output terminals and adapted for amplifying said data signal;

controllable feedback resistance means coupled between said signal input and signal output terminals of said amplifier to form a transimpedance amplifier;

differentiating means coupled to receive said data signal for generating a stream of differentiated pulses including a pulse in response to each transition of said data signal;

rectifying means coupled to said differentiating means for generating undirectional pulses in response to said differentiated pulses; and

control signal generating means coupled to said rectifying means and to said controllable feedback resistance means for generating a control signal for controlling said resistance means to reduce said resistance in response to increases in amplitude and number per unit time of said rectified pulses and to increase said resistance in response to decreases in said amplitude and number per unit time of said rectified pulses whereby said resistance of said feedback resistance means is responsive to the data rate of said data signal for selecting the bandwidth of said transimpedance amplifier.

5. An arrangement according to claim 4 further comprising amplitude limiting means for limiting the amplitude of said differentiated pulses whereby said control signal responds to said number per unit time of said pulses and does not respond to said amplitude of said pulses.

6. An amplifying arrangement for a data signal, comprising:

a gain control voltage amplifier including signal input and signal output terminals and adapted for amplifying said data signal, and also including a gain control input terminal;

feedback means coupled to said signal input and signal output terminals to form a transimpedance amplifier, the resistance of said feedback means being responsive to the data rate of said data signal for selecting the bandwidth of said transimpedance amplifier;

clamping means coupled to said signal output terminal of said voltage amplifier for clamping said data signals to a reference level;

detecting means coupled to said clamping means for generating a peak signal representative of the peak magnitude of said data signals; and

averaging means coupled to said detecting means and to said gain control input terminal of said voltage amplifier for averaging said peak signal for forming a control signal, whereby the amplitude of which is responsive to the amplitude of said data signals at said output terminal of said voltage amplifier whereby a second feedback loop is established for controlling said gain of said voltage amplifier in a manner tending to maintain constant amplitude of said data signals at said output terminal.

7. An arrangement according to claim 6 wherein said voltage amplifier comprises a dual-gate field effect transistor, a first gate of which is coupled to said signal input terminal, and a second gate of which is coupled to said gain control input terminal.

8. An amplifier arrangement adapted for amplifying a bilevel signal from a high impedance source of signal current, comprising:

inverting amplifier means having a relatively high input impedance at an input terminal and a relatively low output impedance at an output terminal for producing an output voltage which equals the input voltage multiplied by a negative constant, said amplifier means having a gain which decreases with increasing frequency;

coupling means coupled to said high impedance source of signal and coupled to said input terminal of said amplifier means for coupling said bilevel signal to said input terminal, said coupling means including an undesired stray capacitance which is effectively coupled across said high impedance of said input terminal and which therefore forms a low pass filter which tends to attenuate high frequency components of said bilevel signal;

differentiating means coupled to said output terminal of said amplifier means for generating ulses during each transition of said bilevel signal, whereby relatively many of said pulses occur per unit time when the data rate of said bilevel signal is large, and relatively few of said pulses occur per unit time when said data rate of said bilevel signal is low, the amplitude of each of said pulses being proportional to the transition speed of said bilevel signal;

averaging means;

rectifying means coupled to said differentiating means and to said averaging means for generating at said averaging means a control signal the magnitude of which depends upon said data rate and said transition speed;

controllable resistance means including a controllable resistance path coupled between said input terminal and said output terminal of said inverting amplifier means, and coupled to said averaging means for receiving said control signal therefrom for decreasing said resistance of said controllable resistance path in response to increases in said amplitude of said control signal, whereby said amplifier means is coupled in a degenerative feedback loop which progressively decreases said gain in response to increases in said amplitude of said control signal whereby the bandwidth of said amplifier means coupled in said feedback loop increases in response to increases in said data rate or in said transition speed or both, and whereby the effective input impedance of said amplifier means coupled in said feedback loop is progressively reduced by increases in said amplitude of said control signal whereby the cutoff frequency of said low pass filter increases thereby reducing said tendency to attenuate high frequency components of said bilevel signal.

9. An arrangement according to claim 8 wherein said inverting amplifier means is a controllable gain amplifier including a gain control input terminal, and further comprising automatic gain control means coupled to said output terminal and to said gain control input terminal for responding to the amplitude of said bilevel signal for controlling the forward gain of said inverting amplifier means for tending to maintain constant amplitude of said bilevel signal.

10. A method for receiving optical data signals comprising the steps of:

applying said optical data signals to a photodiode to produce a data current representative of said data;

applying said data current to a signal input terminal of an inverting voltage amplifier including a feedback resistance to produce an amplified data signal;

producing a transition signal representative of at least some transitions of said data signal;

averaging said transition signal to produce a control signal representative of the data rate; and

controlling said feedback resistance in response to said control signal for varying the bandwidth of said amplifier in response to said data rate; and

wherein said step of producing a transition signal includes a differentiating step.

11. A method for receiving optical data signals comprising the steps of:

applying said optical data signals to a photodiode to produce a data current representative of said data;

applying said data current to a signal input terminal of an inverting voltage amplifier including a feedback resistance to produce an amplified data signal;

producing a transition signal representative of at least some transitions of said data signal;

averaging said transition signal to produce a control signal representative of the data rate; and

controlling said feedback resistance in response to said control signal for varying the bandwidth of said amplifier in response to said data rate; and

wherein said step of producing a transition signal includes a rectification step.