TIMING CIRCUIT

Abstract: Timing circuits are known and can be used to synchronize different circuits to each other. To obtain this, timing circuits with delay means delay an input signal with a predetermined value. To improve the known timing circuit the timing circuit of the invention comprises adjustable delay means, and further uses counting means to count the input signal and the output signal. In this way a simple and more cost effective timing circuit is obtained.

Description: Timing circuit. The invention relates to a timing circuit as described in the preamble of Claim 1. The invention further relates to delay means for use in such a timing circuit. The invention further relates to a method for delaying a clock signal as described in the preamble of Claim 5. The invention further relates to a display device comprising such a timing circuit. Timing circuits having an adjustable delay are known, and can be used in a lot of different devices. For example a timing circuit can be used in LCD projection. These known timing circuits with adjustable delay have as a disadvantage that they cannot delay very high frequencies and/or do not offer a delay range sufficient enough to compensate for the total delay (for example in an analog path) and/or are rather expensive. It is inter alia an object of the invention to obtain a timing circuit and a method for delaying a timing signal that overcomes the drawbacks of the prior art. To this end a first aspect of the invention provides a timing circuit as defined in Claim 1. A second aspect of the invention provides a method of delaying a timing signal as defined in Claim 5. An advantages of a timing circuit and a method for delaying a timing signal according to the invention is that it is possible to obtain a large clock delay range. Further the clock delay can be made frequency independent. The timing circuit according to the invention can delay the clock signal with a very high frequency (for example 200 MHz). Embodiments of the invention are defined in the dependent Claims. The invention and additional features, which may optionally be used to advantage, will be apparent from and elucidated with reference to the examples described below hereinafter and shown in the Figures. Herein shows: Figure 1 a block schematic example of delaying a clock signal. Figure 2 a block schematic example of a timing circuit in more detail. Figure 3 a timing diagram of the timing circuit of Figure 2. Figure 1 shows schematically an example of a timing circuit TC as can be used in a video-processing device of a LCD projection device. At an input il a digital video signal vd is received. This digital video signal is supplied to a D/A converter DA, which D/A converter supplies an analog video signal Va. The output of the D/A converter is coupled to a fixed delay device fd. In this example the fixed delay device fd represents the delay resulting from functions like gamma, contrast, gain adjustment, etc. as normally performed on the analog video signal. The output of the fixed delay device is coupled to a sub-sampler SS, which sub-sampler forms the output O. At another input 12 a clock signal elk is received which clock signal is supplied as a clock signal to the D/A converter DA, to a flip-flop FF and as an input signal to the timing circuit TC. At the other input the timing circuit receives a signal hs in this example a horizontal sync signal from the flip-flop FF. The timing circuit TC comprises a clock delay cd and a sync delay sd and supplies at outputs a delayed clock signal elk-d and a delayed sync signal hs-d. These two output signals are supplied to a sub-sampler controller ssc, which sub-sampler controller controls the switching over of the switch sw of the sub- sampler ss. Every clock cycle the sampling switch sw changes one position although the input of the sub-sampler is analog it does not mean that there are no requirements with relation to the clock phase of the sub-samplers clock. To obtain the best picture, the sampling phase of the sub-samplers clock needs to be correct with relation to the eye pattern of the analog signal. For this reason the clock of the D/A converter DA needs to be delayed. This means that the control signals that control the sub-sampler ssc are also delayed by the same amount. The control signals of the sub-sampler must by synchronized every line. It is assumed that the horizontal input sync pulse its digital signal that can be clocked with CKD in order to synchronize the digital circuitry with pixel accuracy. In order to synchronize the digital circuitry that is running on the delayed clock it is necessary to delay the horizontal synchronization pulse hs also. The delay should be chosen such that valid, set up and hold times are obtained when hs-d is clocked with elk-d. Due to tolerances of the fixed delay in the analog path and in the situation in which a variable clock frequency is used it is not always possible to use a fixed delay for the clock and sync delay. In Figure 2 the timing circuit with the clock delay is shown in more detail and will be described hereinafter. Figure 2 shows a timing circuit TC2 having two input signals being a clock signal elk and a synchronization signal hs. The timing circuit TC2 supplies a delayed clock signal elk-d and a delayed synchronization signal hs-d. This delayed synchronization signal can be used to synchronize other circuitry running on the delayed clock elk-d. To explain the timing circuit TC2 a timing diagram as shown in Figure 3 will be used. In this example of the timing circuit TC2 two counters are used. A first counter CA is running on a clock signal elk where a second counter CB is running on the delayed signal elk-d. In this example the counters count up to five and are reset again. The terminal count tcA of counter CA is delayed by an adjustable delay block ADB resulting in a signal tcAd. Next a PLL (comprising a phase detector PD, a loop filter LF and a voltage control oscillator VCO) controls the phase of the delayed clock signal elk-d such that a rising edge of the terminal count tcb of the second counter CB go insides with the rising edge of the signal tc-A-d. With respect of the terminal count tcB the states of the counter CB are fixed. In this way the two counters are synchronized in such a way that the state of counter CB is a delayed version of the state of counter CA. This means that also the output clock elk-d is a delayed version of the input clock elk. There are various methods to realize a delay between the terminal count signal tcAo of counter CA and the terminal account tcB of counter CB. One possibility is to use existing delay devices. A number of count stage of counter CA and counter CB can however be chosen such that the frequency of the signal tcAo is not out of the range of the delayed device anymore. Another way to realize the delay is to modify the PLL itself, such that the PLL itself introduces the desired delay. In that way no dedicated delay device is necessary anymore. Apart from the clock signal the circuitry also delays the reference signal hs by the same amount, which result in hs-d. A rising edge of hs is determined by an edge detector ED (h int). The state of countA at the moment of the rising edge of hs is stored in the register Rl (res-state). The output of the register Rl supplies a signal rs to a comparator COM. At the other input the comparator receives the signal countB from the counter CB. Next a count interval is defined as the interval in which the counters CA and CB count from zero to their maximum value (in this example 5). The signal resintA indicates the interval just after the interval in which a rising edge of hs was detected. The signal resintB then indicates the corresponding interval for counter CB. The signal resintB is thus a delayed version of resintA where the delay is identical to the delay of the clock signal. Next when resintB is high at the state of counter CB is equal to the res-state the signal hs-d goes high. In this way the delayed synchronization signal is obtained that undergoes the same delay as the clock itself when the delay changes. The signal hint is also supplied to a SR flip-flop SRFF. The output of the SR flip flop is coupled to a second register R2. The output supplying the signal resintA of the register R2 is coupled to the reset input of the SR flip-flop SRFF. The output is further coupled to a third register R3 supplying the signal resintB. The output of the register R3 is coupled to an AND gate AND. At the other input the AND gate receives an output signal from the comparator COM. The output of the AND gate is coupled via a D flip-flop to the output of the timing circuit TC2 for supplying the signal hs-d. It is to be noticed that above a timing circuit and a method of the invention has been described on the basis of an example. The man skilled in the art will be well aware of a lot of variations, which fall within the scope of the present invention.

Claims: CLAIMS: 1. Timing circuit comprising an input for receiving an input signal, delay means for delaying the input signal and an output for supplying an delayed output signal, characterized in that the delay means being adjustable delay means comprising counting means for counting the input signal and the delayed output signal. 2. Timing circuit as claimed in claim 1 characterized in that the counting means comprise a first counter for counting the input signal and a second counter for counting the delayed output signal whereby the outputs of the counters are coupled each to an input of a phase detector for supplying a difference signal. 3. Timing circuit as claimed in claim 1 characterized in that the timing circuit comprises a second input for receiving a second input signal and means for delaying the second input signal with the same delay as the first input signal, and supply at a second output a second delayed output signal. 4. Delay means for use in a timing circuit as claimed in claim one of the claims 1- 3. 5. Method for receiving an input signal, delaying the input signal and supplying an delayed output signal, characterized in that the delaying being an adjustable delaying by counting the input signal and the delayed output signal. 6. Display device for displaying an image comprising a timing circuit as claimed in claim 1.

Inventors: LAMMERS MATHEUS J G, VAN ASMA CORNELIS G M, LAMMERS, MATHEUS, J., G., VAN ASMA, CORNELIS, G., M.
Applicants: KONINKL PHILIPS ELECTRONICS NV, PHILIPS SVENSKA AB, KONINKLIJKE PHILIPS ELECTRONICS N.V., PHILIPS AB
Application year: 1999
Main classification: H03K5
IPC codes: H03K5