GB2039154A - Resistive ladder networks - Google Patents

Abstract

An integrated ladder network designed to equalise the connections made between the elements of the ladder thus making the ladder more accurate comprises a supply terminal (13) in the form of a triangle with a plurality of similar resistance elements (R) being connected thereto in a uniform manner along one side with the free ends thereof interconnected by a plurality of similar resistance elements in a similar manner, such that each element in the network is of the same size and shape and is connected to the adjacent terminal area (A to G) by a connection of the same size and shape. <IMAGE>

Description

SPECIFICATION Improvements in or relating to ladder networks The present invention relates to ladder networks and more particularly to an integrated resistance ladder network.

Known integrated ladder network layout patterns suffer from variable and excessive interconnection track lengths and therefore, by virtue of the variable interconnection resistance the ladder performance degenerates.

Furthermore the power supply connection is also resistive and this causes further innacuracies.

It is an object of the present invention to provide an integrated ladder network which considerably reduces the above disadvantages.

According to the present invention there is provided an integrated resistance ladder network for providing a division of an input voltage into a number of output quantities, including a first plurality of resistors con nected in parallel to a reference voltage sup ply line, the opposite ends of each of the plurality of resistors forming the output termi nals each said output terminal being joined to its neighbouring terminal by a resistor of a second plurality of resistors to provide said ladder network, in which in said integrated circuit layout the reference voltage supply line comprises a relatively large substantially triangular metallic area, in which said first plurality of parallel connected resistors are arranged in a parallel manner along at least one side of said triangular area and are connected directly to said triangular metallic area and in which each of said second plurality of resistors is connected directly to the associated resistor of said first plurality of resistors.

An embodiment of the present invention is shown by way of example with reference to the accompanying drawings.

Figure 1 shows diagrammatically the layout of the integrated ladder network and Fig. 1A shows in greater detail a portion of the ladder network of Fig. 1, Figure 2 shows the electrical circuitry of the integrated ladder network of Fig. 1.

Referring now to Figs. 1 and 1A the integrated layout may be considered to be split into two mirror image halves 10 and 11, both halves being supplied with power via a large area 1 2 within which is a voltage supply lead bonding area 1 3 and which overlaps the resistor areas to form the voltage supply connection as shown by the; continous voltage rail 20 of Fig. 2.

The reference letters in Fig. 1 correspond to the terminal points indicated by the reference letters in Fig. 2.

Fig. 1A shows in greater detail the interconnection method. The metal interconnect patterns are shown at 14, 15, the resistor area at 16 and the contact areas at 17, 18.

It may be seen that the layout offers the following advantages.

(a) Metal interconnection lengths minimised.

(b) Metal interconnection lengths matched.

(c) Resistance in the power supply connection minimised by the use of an equipotential plane.

The layout also achieves the following conventional matching requirements: (a) All resistors are identical in shape (b) All resistors are in the same orientation (c) Contact areas all identical.

1. An integrated resistance ladder network for providing a division of an input voltage into a number of output quantities, including a first plurality of resistors connected in parallel to a reference voltage supply line, the opposite ends of each of the plurality of resistors forming the output terminals, each said output terminal being joined to its neighboring terminal by a resistor of a second plurality of resistors to provide said ladder network, in which in said integrated circuit layout the reference voltage supply line comprises a relatively large substantially triangular metallic area, in which said first plurality of parallel connected resistors are arranged in a parallel manner along at least one side of said triangular area and are connected directly to said triangular metallic area and in which each of said second plurality of resistors is connected directly to the associated resistor of said first plurality of resistors.

2. An integrated resistance ladder network as claimed in claim 1 in which each connection between one of said first plurality of resistors to a respective one of said second plurality of resistors is by a connecting pad, the area of connecting pad on each resistor being substantially the same, and in which the length of and width of each connecting pad between each respective resistor is also substantially the same.

3. An integrated resistance ladder network as claimed in claim 1 or claim 2 in which each resistor comprises a substantially rectangular area of resistive material.

4. An integrated resistance ladder network as claimed in claim 2 in which each resistor is arranged to have its longest side substantially parallel to the longest side of each other resistor.

5. An integrated resistance ladder network substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to ladder networks The present invention relates to ladder networks and more particularly to an integrated resistance ladder network. Known integrated ladder network layout patterns suffer from variable and excessive interconnection track lengths and therefore, by virtue of the variable interconnection resistance the ladder performance degenerates. Furthermore the power supply connection is also resistive and this causes further innacuracies. It is an object of the present invention to provide an integrated ladder network which considerably reduces the above disadvantages. According to the present invention there is provided an integrated resistance ladder network for providing a division of an input voltage into a number of output quantities, including a first plurality of resistors con nected in parallel to a reference voltage sup ply line, the opposite ends of each of the plurality of resistors forming the output termi nals each said output terminal being joined to its neighbouring terminal by a resistor of a second plurality of resistors to provide said ladder network, in which in said integrated circuit layout the reference voltage supply line comprises a relatively large substantially triangular metallic area, in which said first plurality of parallel connected resistors are arranged in a parallel manner along at least one side of said triangular area and are connected directly to said triangular metallic area and in which each of said second plurality of resistors is connected directly to the associated resistor of said first plurality of resistors. An embodiment of the present invention is shown by way of example with reference to the accompanying drawings. Figure 1 shows diagrammatically the layout of the integrated ladder network and Fig. 1A shows in greater detail a portion of the ladder network of Fig. 1, Figure 2 shows the electrical circuitry of the integrated ladder network of Fig. 1. Referring now to Figs. 1 and 1A the integrated layout may be considered to be split into two mirror image halves 10 and 11, both halves being supplied with power via a large area 1 2 within which is a voltage supply lead bonding area 1 3 and which overlaps the resistor areas to form the voltage supply connection as shown by the; continous voltage rail 20 of Fig. 2. The reference letters in Fig. 1 correspond to the terminal points indicated by the reference letters in Fig. 2. Fig. 1A shows in greater detail the interconnection method. The metal interconnect patterns are shown at 14, 15, the resistor area at 16 and the contact areas at 17, 18. It may be seen that the layout offers the following advantages. (a) Metal interconnection lengths minimised. (b) Metal interconnection lengths matched. (c) Resistance in the power supply connection minimised by the use of an equipotential plane. The layout also achieves the following conventional matching requirements: (a) All resistors are identical in shape (b) All resistors are in the same orientation (c) Contact areas all identical. CLAIMS

1. An integrated resistance ladder network for providing a division of an input voltage into a number of output quantities, including a first plurality of resistors connected in parallel to a reference voltage supply line, the opposite ends of each of the plurality of resistors forming the output terminals, each said output terminal being joined to its neighboring terminal by a resistor of a second plurality of resistors to provide said ladder network, in which in said integrated circuit layout the reference voltage supply line comprises a relatively large substantially triangular metallic area, in which said first plurality of parallel connected resistors are arranged in a parallel manner along at least one side of said triangular area and are connected directly to said triangular metallic area and in which each of said second plurality of resistors is connected directly to the associated resistor of said first plurality of resistors.

2. An integrated resistance ladder network as claimed in claim 1 in which each connection between one of said first plurality of resistors to a respective one of said second plurality of resistors is by a connecting pad, the area of connecting pad on each resistor being substantially the same, and in which the length of and width of each connecting pad between each respective resistor is also substantially the same.

3. An integrated resistance ladder network as claimed in claim 1 or claim 2 in which each resistor comprises a substantially rectangular area of resistive material.

4. An integrated resistance ladder network as claimed in claim 2 in which each resistor is arranged to have its longest side substantially parallel to the longest side of each other resistor.

5. An integrated resistance ladder network substantially as described with reference to the accompanying drawings.