EP0196694A1
Expired / Lapsed
EP
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Picture display device
Assignee: Koninklijke Philips NV
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Filing: 1986-03-03
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Granted: —
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Expires: 2006-03-03
Abstract
Abstract The distortion of an emitter-follower output stage (35, 37) of a video amplifier for driving a cathode of a picture display tube (14) can be reduced without rendering a beam current control via this output stage impossible, by using a low-distortion buffer stage (58) for producing a negative feedback signal at the output of the output stage (Figure 1). A higher follow rate for small signal variations can be obtained with the aid of a bias current (59) or quiescent current which then is subtracted again from the current applied to an input (43) of a beam measuring circuit (9) which is controlled by the output stage.
Inventors
- 👤 Pieter Gerrit Blanken
- 👤 Pieter Van Der Zee
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-09 15:01
CPC Classifications
H; H04; H04N; H04N3/00; H04N3/10; H04N3/16; H04N3/22; H04N5/00; H04N5/44; H04N5/57; H04N5/59
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
97 words
A picture display device comprising a picture display tube (41) a cathode of which is coupled to an emitter-follower (37) drivable by a video preamplifier, a negative feedback signal input (fase 21) of the video preamplifier being coupled to an output (45) of a negative feedback circuit and the collector of the emitter-follower being coupled to an input (43) of a beam current measuring circuit (9), characterized in that the negative feedback signal input (base 21) is coupled to an output (51) of a substantially distortion-free buffer stage (58) which is drivable by the emitter-follower (35, 37).
Claim 2
Dependent Claim
97 words
A picture display device comprising a picture display tube (41) a cathode of which is coupled to an emitter-follower (37) drivable by a video preamplifier, a negative feedback signal input (fase 21) of the video preamplifier being coupled to an output (45) of a negative feedback circuit and the collector of the emitter-follower being coupled to an input (43) of a beam current measuring circuit (9), characterized in that the negative feedback signal input (base 21) is coupled to an output (51) of a substantially distortion-free buffer stage (58) which is drivable by the emitter-follower (35, 37).
Claim 3
Dependent Claim
92 words
A picture display device as claimed in Claim 1, in which an anti-blocking circuit (59) is coupled to the cathode of the picture display tube (41) to prevent blocking of the beam current measuring circuit due to leakage currents of the display tube, characterized in that the anti-blocking circuit is a circuit (59) which produces an emitter-follower current of the order of magnitude of at least approximately one hundred micro-amperes, whilst a current source for discharging the emitter-follower current is coupled to the input (43) of the beam current measuring circuit (9).
Claim 4
Dependent Claim
94 words
A picture display device as claimed in Claim 2, characterized in that the emitter-follower (37) is part of a complementary emitter-follower circuit (35, 37) which further comprises an emitter-follower (35) which is complementary to said emitter-follower, the anti-blocking circuit is a bias voltage circuit (60, 61) for the bases of the emitter-followers,and the current source is a further current mirror circuit (69), an input (67) of which is coupled to an output (65) of a current mirror circuit (63), an input (62) of which is coupled to the collector of the complementary emitter-follower (35).
Claim 5
Dependent Claim
77 words
A picture display device as claimed in Claim 3, characterized in that the input (62) of the current-mirror circuit (63) is connected to the negative feedback input (73) of an amplifier (75) whose output (77) is connected to the negative feedback input (73) via a unidirectionally conducting element (79) and a further input (81) is connected to a connection of a current source (83) and a similar impedance (85) as the impedance of the current-mirror circuit (63).
Claim 6
Dependent Claim
26 words
A picture display device as claimed in anyone of the preceding Claims, characterized in that the buffer stage (58) is a complementary emitter-follower circuit (53, 55).
References Cited (Backward Citations)
GB2014408A
Cited
WO1982003147A1
Cited
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