# Memories

 Question 1
A 2$\times$ 2 ROM array is built with the help of diodes as shown in the circuit below. Here W0 and W1 are signals that select the word lines and B0 and B1 are signals that are output of the sense amps based on the stored data corresponding to the bit lines during the read operation.
During the read operation, the selected word line goes high and the other word line is in a high impedance state. As per the implementation shown in the circuit diagram above, what are the bits corresponding to $D_{ij}$ (where i = 0 or 1 and j = 0 or 1) stored in the ROM?
 A $\begin{bmatrix} 1 & 0\\ 0 & 1 \end{bmatrix}$ B $\begin{bmatrix} 0 & 1\\ 1 & 0 \end{bmatrix}$ C $\begin{bmatrix} 1 & 0\\ 1 & 0 \end{bmatrix}$ D $\begin{bmatrix} 1 & 1\\ 0 & 0 \end{bmatrix}$
GATE EC 2018   Digital Circuits
Question 1 Explanation:

$\begin{array}{l} \text { When, } W_{0}=V_{D O}, B_{0}=V_{D D} \text { ; otherwise } B_{0}=0 \\ \text { When } W_{1}=V_{D O} B_{1}=V_{D D} \text { ; otherwise } B_{1}=0 \\ \text { So, } B_{0}=W_{0} \text { and } B_{1}=W_{1} \\ \text { Hence } \begin{array}{c|cc} &B_{0}&B_{1}\\ \hline W_{0}&1&0\\ W_{1}&0&1 \end{array}\\ \end{array}$
 Question 2
In a DRAM,
 A periodic refreshing is not required B information is stored in a capacitor C information is stored in a latch D both read and write operations can be performed simultaneously
GATE EC 2017-SET-2   Digital Circuits
Question 2 Explanation:
In a DRAM, data is stored in the form of charge on capacitor and periodic refreshing is needed to restore the charge on capacitor.
 Question 3
If WL is the Word Line and BL the Bit Line, an SRAM cell is shown in
 A A B B C C D D
GATE EC 2014-SET-3   Digital Circuits
Question 3 Explanation:

 Question 4
In the circuit shown in the figure, A is parallel-in, parallel-out 4 bit register, which loads at the rising edge of the clock C . The input lines are connected to a 4 bit bus, W. Its output acts at input to a 16$\times$4 ROM whose output is floating when the enable input E is 0. A partial table of the contents of the ROM is as follows

The clock to the register is shown, and the data on the W bus at time $t_{1}$ is 0110. The data on the bus at time $t_{2}$ is
 A $1111$ B $1011$ C $1000$ D $0010$
GATE EC 2003   Digital Circuits
Question 4 Explanation:
When W has data 0110 i.e. 6 in decimal its data value at that add. is 1010.
Now 1010 i.e. 10 is acting as add. at time $t_{2}$ and data at that moment is 1000.
 Question 5
If the input $X_3, X_2, X_1, X_0$ to the ROM in figure are 8-4-2-1 BCD numbers, then the outputs $Y_3Y_2Y_1Y_0$ are
 A gray code numbers B 2-4-2-1 BCD numbers C excess 3 code numbers D none of the above
GATE EC 2002   Digital Circuits
Question 5 Explanation:
$\begin{array}{ccccccccc} &&&&4&3&2&1&\\ x_{3} & x_{2} & x_{1} & x_{0} & y_{3} & y_{2} & y_{1} & y_{0} & \\ 0 & 0 & 0 & 0 & 0 & 0 & 0 & 0 & \rightarrow 0 \\ 0 & 0 & 0 & 1 & 0 & 0 & 0 & 1 & \rightarrow 1 \\ 0 & 0 & 1 & 0 & 0 & 0 & 1 & 0 & \rightarrow 2 \\ 0 & 0 & 1 & 1 & 0 & 0 & 1 & 1 & \rightarrow 3 \\ 0 & 1 & 0 & 0 & 0 & 1 & 0 & 0 & \rightarrow 4 \\ 0 & 1 & 0 & 1 & 0 & 1 & 0 & 1 & \rightarrow 5 \\ 0 & 1 & 1 & 0 & 1 & 1 & 0 & 0 & \rightarrow 6 \\ 0 & 1 & 1 & 1 & 1 & 1 & 0 & 1 & \rightarrow 7 \\ 1 & 0 & 0 & 0 & 1 & 1 & 1 & 0 & \rightarrow 8 \\ 1 & 0 & 0 & 1 & 1 & 1 & 1 & 1 & \rightarrow 9 \end{array}$
$\therefore \text{ is }8421BCD\text{ to }2421BCD$
 Question 6
In the DRAM cell in figure, the $V_{t}$ of the NMOSFET is 1 V. For the following three combinations of WL and BL voltages.
 A 5 V; 3V; 7V B 4 V; 3V; 4V C 5 V; 5V; 5V D 4 V; 4V; 4V
GATE EC 2001   Digital Circuits
There are 6 questions to complete.