Browse Prior Art Database

Bucket Brigade Charge Packet Diverter

IP.com Disclosure Number: IPCOM000084936D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Heller, LG: AUTHOR

Abstract

The charge packet diverting function is an important operation in many signal processing applications of charge-transfer devices. Although diverting packets in charge-coupled devices (CCD's) is essentially error free, implementation in the currently available bucket brigade (BBD) technology has an error due to threshold mismatch in the BBD devices. The cause of this error can be seen by considering the standard BBD diverter indicated in Fig. 1.

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Bucket Brigade Charge Packet Diverter

The charge packet diverting function is an important operation in many signal processing applications of charge-transfer devices. Although diverting packets in charge-coupled devices (CCD's) is essentially error free, implementation in the currently available bucket brigade (BBD) technology has an error due to threshold mismatch in the BBD devices. The cause of this error can be seen by considering the standard BBD diverter indicated in Fig. 1.

After transferring the electronic charge packet Q through device T(a) onto node A1, the diverter operation is performed by then transferring Q onto node A2 or node A3 by activating phase Phi'(b) or Phi(b), respectively. If Q is transferred onto node A3, for example, and the previous packet was also transferred onto node A3, then there is no error. However, if the previous packet was transferred onto node A2, an error in charge equal to +/- (V(th1) - V(th2))C results from the mismatch in the threshold voltages of devices T1 and T2. For some allowable signal voltage Delta V = Q/C, the fractional diversion error is given by: DE (standard diverter) = +/- (V(th1 - V(th2))C/Q = +/- (V(th1) - V(th2)/DeltaV. (1).

Since Delta V(th) = (V(th1) - V(th2)) is often in the > 20 - 50 mV range, the resulting error can be a major problem in analog signal processing applications (such as analog/digital (A/D) converters).

The diversion error can be substantially reduced by using a mixture of CCD and BBD concepts. The proposed solution is shown in Figs. 2A, 2B, and 2C. In the circuit of Fig. 2A, the charge packet to be diverted, Q, is first transferred and stored Partially in an inversion layer of capacitance C(g) and partially on two diffusions of capacitances C(d). The diverting operation is then performed by transferring Q out through the BBD devices T1 or T2. However, in this circuit the large inversion capacitance C(g) (C(g) is a large part of the storage node capacitance) does not contribute to the diversion error.

The reduced diversion error can be explained from the surface potential plots shown in Figs. 2B and 2C. In these plots, the cross-hatched regions represent carriers on the diffusions below the V(g) - V(th) barriers, where V(g) is the amplitude of the BBD phase pulses. The Packet Q is rep...