barcode fonts for ssrs But and in Software

Drawer Code 3 of 9 in Software But and

(2) (3)

CHAP. 7]

Fig. 7-24

Substituting (2) and (3) into (1) and rearranging give     V Yin s Cgk 1 o Cpg VS Now, from the result of Problem 7.21, Vo RL VS RL rp so (4) becomes     RL Yin s Cgk 1 C RL rp pg

(b) The output admittance is Yo and I2 Ip Ipk IL Vo Vo Ipk sCpk Vo 7 (8)

Let Yo0 be the output admittance that would exist if the capacitances were negligible; then  so that (c) Yo s Ip Yo0 Vo   R L rp 1 Cpg Cpk Yo0 RL 9 (10)

From (6) and (10) we see that high-frequency triode operation can be modeled by Fig. 7-9(b) with a capacitor Cin Cgk 1 RL = RL rp Cpg connected from the grid to the cathode, and a capacitor Co 1 RL rp =RL Cpg Cpk connected from the plate to the cathode.

7.24 7.25 Find the input impedance as seen by the source vi of Example 4.2 if CC is large. Ans: 940 k

Show that the p transconductance of a JFET varies as the square root of the drain current. p Ans: gm 2 IDSS =Vp0 iD

In the ampli er of Fig. 4-15, R1 20 k; R2 100 k; R3 1 M; rds 30 k;  150 (see Problem 7.2), and RS 1 k. Find (a) Av vo =vi ; b Ai id =ii , and (c) Zo . Ans: a 0:829; b 843; c 198:7  Find the voltage gain of the CG ampli er of Fig. 7-13(a). Ans: Av vo =vi  1 RD = RD rds  1 RS Find the voltage gain Av2 v2 =vi for the circuit of Fig. 7-25(a). Figure 7-25(b) is a small-signal equivalent circuit in which impedance re ection has been used for simpli cation. Ans: Av2 RD = RD rds  1 RS Let RL1 RL2 ! 1 for the ampli er of Fig. 7-25(a). If RD RS , the circuit is commonly called a phase splitter, since v2 v1 (the outputs are equal in magnitude but 1808 out of phase). Find Av1 v1 =vi and, by comparison with Av2 of Problem 7.28, verify that the circuit actually is a phase splitter. Ans: Av1 RS = RD rds  1 RS For the circuit of Fig. 7-25(a), model the MOSFET by NMOSG of Example 4.4 except use Vto 4 V. Let VGG 2 V, VDD 15 V; RD RS 1:5 k; RL1 RL2 10 k, and CC1 CC2 100 F. Use SPICE analysis to show that v1 v2 , thus substantiating the claim of Problem 7.29 that the circuit is a phase splitter. (Netlist code available from author website.)

L2 _

L2 _

Fig. 7-25 For the ampli er circuit of Example 7.4, reduce the value of the bypass capacitor CS to 0:01 F so that RS no longer appears shorted to ac signals and assess the impact on voltage gain. (Netlist code available from author website.) Ans: Av 1:22 1398 The series-connected JFETs of Fig. 4-23 are identical, with  70; rds 30 k; RG 100 k; and RD RL 4 k. Find (a) the voltage-gain ratio Av vL =vi ; b the current-gain ratio Ai iL =ii , and (c) the output impedance Ro . Ans: a Av 9:32; b Ai 233; c Ro 2:16 M The JFET ampli er of Fig. 4-33 has RG 1 M; RS1 800 ; RS2 1:2 k; and RL 1 k. The JFET obeys (4.2) and is characterized by IDSS 10 mA, Vp0 4 V; VGSQ 2 V; and  60. Determine (a) gm by use of (7.3), (b) rds , and (c) the voltage-gain ratio Av vL =vi . Ans: a 2:5 mS; b 24 k; c 0:52

CHAP. 7]